JPH10264426A - Printer and printing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate shift of color and registration by eliminating difference of carrying speed due to difference of the diameter of capstan roller thereby equalizing the width of all lines. SOLUTION: At each print stage 10, 20, 30, a color thermal recording sheet 1 is carried by a capstan roller 13a, 23a, 33a being rotated through a first, second or third motor 15, 25, 35. Each motor driver 41-43 drives microstepping of a corresponding motor. In the microstep driving, a step sequence is repeated at a period corresponding to the diameter of a corresponding capstan roller and the period of step sequence is regulated by increasing/decreasing the number of times of microstep sequence being executed during one step sequence. The capstan roller is rotated at a rotational speed corresponding to the diameter thereof through microstep driving and the carrying speed of color thermal recording sheet 1 is equalized for all print stages 10, 20, 30. Consequently, the carrying amount per line is equalized for all print stages and the line width is equalized for all colors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a printing method and apparatus for recording an image on recording paper.

[0002]

2. Description of the Related Art A printer which records a color image on a recording sheet while moving a recording head and a recording sheet relatively is known. For example, a color thermal printer uses a color thermal recording paper in which a cyan thermal coloring layer, a magenta thermal coloring layer, and a yellow thermal coloring layer are sequentially formed on a support. While moving, the thermal recording paper is heated by the thermal head to record a full-color image. In the thermal head, a large number of heating elements are formed on a line, and an image of one color is recorded line by line.

In such a color thermal printer, in order to perform high-speed printing, three thermal heads are arranged in a pass area (transport path) of the color thermal recording paper, and the color thermal recording paper is placed on the upstream side of the transport path. From one to the downstream side
There is a three-head one-pass system in which a yellow image, a magenta image, and a cyan image are sequentially recorded on a print stage by each thermal head to record a full-color image.

[0004]

By the way, in this three-head one-pass type color thermal printer, for example, the pulse rate of a step (pulse) motor for driving the capstan roller of each print stage is made the same, and The color thermosensitive recording paper is transported at the same transport speed within the printer. Although each capstan roller is manufactured so that its diameter is constant, the diameter of the capstan roller varies due to manufacturing errors. If the diameter of the capstan roller used in each print stage varies, even if each step motor is driven at the same rotational speed, the transport speed of the color thermosensitive recording paper at each print stage, that is, per unit time Will be different. If a difference occurs in the transport amount of the color thermal recording paper per unit time between the respective print stages, even if the recording start positions of the images of the respective colors are matched at the start of recording, the difference is accumulated and one screen is recorded. The recording position at the portion differs for each color. As a result, there has been a problem that color misregistration or registration misregistration occurs, thereby deteriorating image quality.

[0005] Further, by temporarily changing the pulse rate of the step motor at appropriate intervals to increase or decrease the width of some of the lines recorded on the recording paper,
The present applicant has proposed a method for reducing color misregistration and preventing occurrence of misregistration (Japanese Patent Application No. 8-28878).
No. 0). However, in this method, if the interval of changing the pulse rate is large, the width of the line becomes extremely narrow or wide, and the density of the line becomes black or black. White streaks may occur. In addition, since the paper is not always transported at a constant transport speed, strictly speaking, a color shift occurs for each line.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a printing method and apparatus capable of preventing occurrence of color misregistration and registration misregistration.

[0007]

According to the printing method of the present invention, a step sequence is periodically performed with a predetermined phase difference for each phase of a step motor, and a predetermined current is supplied in one step sequence. By performing a plurality of micro-step sequences that flow for a fixed time, and gradually increasing and then decreasing the drive current supplied to each phase, the respective step motors are micro-step driven, and each step is performed. For each motor, the number of micro-step sequences in one step sequence is determined according to the diameter of the corresponding capstan roller, and the cycle of the step sequence is adjusted. Are matched with each other.

In a printing method according to a second aspect of the present invention, a captan roller is provided for each thermal head, and the thermal head records a specific color line by line while the recording paper is being conveyed by the corresponding captan roller. It is.

In the printing apparatus according to the third aspect, a step sequence is periodically performed with a predetermined phase difference for each phase of the step motor, and in one step sequence,
By performing a plurality of microstep sequences in which a predetermined current is passed for a predetermined time, the drive current supplied to each phase is increased stepwise and then decreased stepwise, thereby driving each of the step motors in a microstep manner. And a motor driver for each step motor in which the number of micro step sequences in one step sequence is determined according to the diameter of the corresponding capstan roller and the cycle of the step sequence is adjusted. The recording paper conveyance speeds are made to match each other.

In a printing apparatus according to a fourth aspect of the present invention, a captan roller is provided for each thermal head, and the thermal head records a specific color one line at a time while the recording paper is being conveyed by the corresponding captan roller. It is.

[0011]

FIG. 1 shows a three-head one-pass color thermal printer embodying the present invention.
The color thermosensitive recording paper 1 is pulled out from a rolled recording paper roll by a paper feeding mechanism (not shown), and sent to a linear conveyance path 3 via a guide roller pair 2. The transport path 3 is provided with a yellow print stage 10, a magenta print stage 20, and a cyan print stage 30 at appropriate intervals in order from the upstream side (left side in the figure).

The color thermosensitive recording paper 1 has a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer having a light fixing property on 365 nm ultraviolet rays, and a yellow thermosensitive coloring layer having a light fixing property on 420 nm ultraviolet rays on a support. They are layered in order. These thermosensitive coloring layers are provided in the order of thermal recording. For example, when thermal recording is performed in the order of magenta, yellow, and cyan, the yellow thermosensitive coloring layer and the magenta thermosensitive coloring layer are interchanged. .

The yellow print stage 10 is a rotatable platen roller 11 that rotates following the conveyance of the color thermosensitive recording paper 1, and is disposed opposite to the platen roller 11, and a yellow thermal stage for recording a yellow image. The head 12 includes a first transport roller pair 13, and a yellow optical fixing device 14 disposed between the yellow thermal head 12 and the first transport roller pair 13.

Below the yellow thermal head 12, a number of heating elements are provided in the sub-scanning direction (color thermal recording paper 1).
The heating element arrays 12a are arranged in a single row in the width direction of the heating element array. The thermal head 12 has a pressing position where the heating element array 12a is pressed against the color thermosensitive recording paper 1 on the platen roller 11 to record an image, and a retracting position where the heating element array 12a is separated from the color thermosensitive recording paper 1. It is movable between and. The yellow optical fixing device 14 has a wavelength peak of 42 after the yellow image is recorded.
The color thermosensitive recording paper 1 is irradiated with ultraviolet light of 0 nm to optically fix the yellow thermosensitive coloring layer.

One of the first transport roller pairs 13 is a capstan roller 13a driven by a first motor 15,
The other is a pinch roller 13b that rotates following the conveyance of the color thermosensitive recording paper 1. The pinch roller 13b is movable between a nip position where the color thermal recording paper 1 is nipped with the capstan roller 13a and a nip release position away from the color thermal recording paper 1. The conveying roller pair 13 conveys the color thermosensitive recording paper 1 in the yellow print stage 10 from the upstream to the downstream by the rotation of the capstan roller 13 a by the first motor 15, and sends it to the magenta print stage 20.

The magenta print stage 20 has the same structure as the yellow print stage 10, and includes a platen roller 21, a magenta thermal head 22 for recording a magenta image, a second conveying roller pair 23, and a magenta light And a fixing unit 24. A heating element array 22a is formed on the magenta thermal head 22. The magenta light fixing device 24 fixes the magenta thermosensitive coloring layer by irradiating the color thermosensitive recording paper 1 with ultraviolet light having a wavelength peak of 365 nm after recording the magenta image. One of the second transport roller pairs 23 is a second transport roller pair.
The capstan roller 23a is driven by the motor 25, and the other is the pinch roller 23b. The transport roller pair 23 transports the color thermosensitive recording paper 1 in the magenta print stage 20 from upstream to downstream and sends it to the cyan print stage 30.

The cyan print stage 30 includes a platen roller 31, a cyan thermal head 32 for recording a cyan image, and a third transport roller pair 33. A heating element array 32a is formed on the thermal head 32 for cyan. The third transport roller pair 33 is
Capstan roller 23a driven by third motor 35
And the pinch roller 33b, which conveys the color thermosensitive recording paper 1 in the cyan print stage 30 from the upstream to the downstream, and sends the color thermosensitive recording paper 1 to the downstream paper discharge mechanism (not shown). .

The system clock generating circuit 5 generates a system clock at a constant cycle Tc. The system controller 6 controls each unit based on the system clock and generates a timing signal for recording one line. This timing signal is generated every four periods of the system clock (4 · Tc) and sent to the recording circuit 7.

The recording circuit 7 drives each of the thermal heads 12, 22, 32 each time a timing signal is inputted,
An image of a color corresponding to the color thermosensitive recording paper 1 being conveyed is recorded line by line. As a result, a full-color image is sequentially recorded on the color thermosensitive recording paper 1 in three color planes, and the portion of the recorded color thermosensitive recording paper 1 is separated and discharged for each image by a paper discharging mechanism.

As the first to third motors 15, 25 and 35, for example, two-phase stepping motors are used, and the first motor driver 41, the second motor driver 42 and the third motor driver 43 respectively correspond to the micro motors. Step driven. Each of the motor drivers 41 to 43 is controlled by the system controller 6 and drives a corresponding motor in synchronization with a system clock from the system clock generation circuit 45.

Each of the motor drivers 41 to 43 performs a step sequence in which the phases of the A phase, A bar phase, B phase, and B bar phase are shifted from each other in order to microstep drive the corresponding motor. . Also,
In each step sequence, the A phase, A bar phase, B phase
, The drive current of the B bar phase is increased stepwise and then decreased stepwise. Thereby, for example, compared with the case of driving by the two-phase excitation method or the 1-2-phase excitation method. The rotation angle of the rotor of the motor is controlled finely.

By increasing or decreasing the number of microstep sequences executed in one step sequence, the cycle of the step sequence is adjusted, and the motor is rotated at a speed corresponding to the diameter of the capstan roller. Thereby, each print stage 10, 20, 30
Is adjusted to the designed transport speed Vp. Then, each transport roller pair 13,
By making the transport speed of the color thermosensitive recording paper 1 by the same 23, 33, the transport amount for one line in each color print stage is made the same, thereby preventing the occurrence of registration shift and color shift.

The first motor driver 41 includes a first motor 1
A-phase circuit 4 for supplying drive current to A-phase and A-bar phase to 5
1a and a B-phase circuit 41b for supplying a drive current to the B-phase and the B-bar phase. Similarly, for the second motor driver 42 and the third motor driver 43,
Each is composed of an A-phase circuit and a B-phase circuit.

FIG. 2 A-phase circuit 4 of first motor driver 41
1a is shown. The system clock from the system clock generation circuit 5 is sent to the sequence data generation circuit 50 and the latch circuit 51. Sequence data generation circuit 50
Is composed of a counter 50a and a ROM 50b. In the ROM 50b, a sequence data group in which a plurality of sequence data is set is written.

Each sequence data is composed of 4 bits, of which Ph bits (first bits) are
“1” indicates that the drive current is supplied to the A-phase coil 16 of the first motor 15, and “0” indicates that the drive current is supplied to the A-bar phase coil 17. The a to c bits (second to fourth bits) are used to control the rotation angle of the rotor 15a of the first motor 15 by a combination of these three bits of logic (“1” or “0”). This represents the reference voltage used. The reference voltage is 4% of V0 (= 0V), 35% V1, 75% V2, 100% V3 (= VREF) with respect to a predetermined voltage VREF.
There are types.

The number of sequence data constituting one set of sequence data group is the same as the sum of the number of times of each micro step sequence of the A phase and the A bar phase executed during one step sequence. It is adjusted by the actual diameter of the capstan roller 13a of the transport roller pair 13 in the yellow print stage 10. The details of this sequence data group will be described later.

The counter 50a increments its count value by one each time one system clock is input. The counter 50a cyclically counts the number of system clocks. After the number of system clocks equal to the number of sequence data written in the ROM 50b, the count value returns to "0" again. . Therefore, this counter 50
The one corresponding to the sequence data group of the ROM 50b provided together with the sequence data generation circuit 50 is used. The counter 50b outputs the count value to RO
Send to M50b.

The ROM 50b uses the count value of the counter 50a as an address and reads out sequence data at that address. Thus, each sequence data of the sequence data group is cyclically read from the ROM 50b. The ROM 50b sends the read sequence data to the latch circuit 51.

The latch circuit 51 latches the sequence data from the ROM 50b every time the system clock is input. The latch circuit 51 uses the reference voltage selecting circuit 5
2, sent to the ON signal generation circuit 53 and the OR circuit 54. The Ph bit of the latched sequence data is supplied to the A-phase AND circuit 55 and the NOT circuit 56.
Is sent to the A-bar phase side AND circuit 57 via.

The voltage VREF is input to the reference voltage selection circuit 52 from a power supply device. This reference voltage selection circuit 5
2 divides the voltage VREF into reference voltages V1, V2, V3
Voltage dividing circuit for extracting the reference voltages V1 and V
2, a selection circuit for selecting and outputting one of V3 and V3 in accordance with the logic combination of the a to c bits. Thereby, the reference voltage selection circuit 52 outputs the reference voltages V1, V2, and V3 according to the sequence data latched by the latch circuit 51. Note that the reference voltage V
When the sequence data corresponding to 0 is latched by the latch circuit 51, that is, when the logic of the a to c bits is all "0", no voltage is output from the selection circuit, and as a result, the reference voltage selection circuit Reference numeral 52 outputs the reference voltage V0.

The OR circuit 54 prevents the drive current from flowing through the A-phase coil 16 and the A-bar phase coil 17 when the sequence data latched by the latch circuit 51 indicates the reference voltage V0. Yes, the result of calculating the logical sum of the a to c bits of the sequence data is sent to the A-phase side AND circuit 55 and the A-bar side AND circuit 57 as a phase control signal.

The A-phase side AND circuit 55 receives the phase control signal from the OR circuit 54, the ON signal from the ON signal generation circuit 53, and the Ph bit from the latch circuit 51,
The logical product of these signals is used as the A-phase drive signal and the A-phase coil 16
To the FET 61 connected to the A-bar phase side AN
D circuit 57 receives the phase control signal from OR circuit 54 and ON
The ON signal from the signal generation circuit 53 and the Ph bit whose logic has been inverted by the NOT circuit 56 are input, and the logical product of these signals is sent to the FET 62 connected to the A bar phase coil 17 as an A bar phase drive signal. The FETs 61 and 62 are turned on while the drive signal is being input, and a drive current flows through the corresponding coils 16 and 17.

Thus, the sequence data in which the Ph bit is "1" and the reference voltage indicates one of V1, V2 and V3 is latched by the latch circuit 51, and
The drive current flows through the A-phase coil 16 while the N signal is being generated. Further, while the Ph bit is “0” and the sequence data indicating the reference voltage is one of V1, V2, and V3 is latched by the latch circuit 51 and the ON signal is generated, the A bar phase coil 17 The drive current flows through.

When performing the micro-step driving, the position of the rotor with respect to the stator (stator) on which the coils of each phase are wound is determined according to the magnitude of the driving current flowing through the coils. In addition, it is necessary to constantly adjust the drive current flowing through each of the coils 16 and 17. To perform this adjustment, an ON signal generation circuit 53, a current detection resistor 63, and a comparator 64 are provided.

The current detection resistor 63 is connected in series with the A-phase coil 16 and the A-bar phase coil 17 and converts the magnitude of the drive current flowing through each of the coils 16 and 17 into a voltage (hereinafter referred to as a detection voltage). And output. Current detection resistor 63
Is proportional to the magnitude of the drive current, the detection voltage increases as the drive current increases. This detection voltage is input to the inverting input terminal of the comparator 64. The reference voltage from the reference voltage selection circuit 52 is input to the non-inverting input terminal of the comparator 64. The comparator 64 compares the detection voltage with the reference voltage, and sends a comparison signal of a signal level corresponding to the comparison result to the ON signal generation circuit 53. In this comparison, when the detected voltage is smaller than the reference voltage, the comparison signal becomes “H level”, and when it is larger, the comparison signal becomes “L level”.

The ON signal generation circuit 53 includes a latch circuit 51
Every time bits a to c of the sequence data are input, the time Tc is the same as the generation cycle of the system clock.
The N signal is generated, but the generation of the ON signal is stopped for an appropriate time each time the comparison signal from the comparator 64 becomes “L level”, and then the ON signal is generated again. This O
The N signal is input to the A-phase AND circuit 55 and the A-bar phase AND circuit 57.

Thus, during each micro-step sequence, the detection voltage detected by the current detection resistor 63 is maintained at the reference voltage determined by the sequence data, and the A-phase coil 16 and the A-bar phase coil 17 are driven. Current is supplied. That is, during each micro-step sequence, a drive current of a constant magnitude corresponding to the four-stage reference voltage is supplied to and maintained in the A-phase coil 16 and the A-bar phase coil 17. In the case of the reference voltage V0, the magnitude of the drive current is “0”. Also, in the following description,
The magnitudes of the driving currents corresponding to the four levels of reference voltages V0, V1, V2, and V3 will be described as I0, I1, I2, and I3.

FIG. 3 schematically shows the contents of the ROM 50b of the A-phase circuit 41a. Note that FIG. 3 also shows a value in which the sequence data is represented by a hexadecimal number and a reference voltage represented by the value. The sequence data group shown in FIG. 3 is used when the diameter of the capstan roller 13a of the transport roller pair 13 is a design value (hereinafter, this is referred to as a standard sequence data group).

The standard sequence data group includes A-phase data and A-phase data.
It consists of a total of 16 sequence data of 8 each for the bar phase. In the standard sequence data group, sequence data at addresses “0” to “7” correspond to the A-phase, and sequence data at addresses “8” to “15” correspond to the A-bar phase. Address “0”,
Each of the sequence data “1”, “8”, and “9” represents the reference voltage V0 by its a to c bits. Similarly, the sequence data of the addresses “2”, “7”, “10”, and “15” are obtained by converting the reference voltage V1 to the sequence data of the addresses “3”, “6”, “11”, and “14”. The data uses the reference voltage V2 as the address “4”, “5”, “1”.
Each of the sequence data "2" and "13" represents the reference voltage V3.

When this standard sequence data group is used, considering the case of the reference voltage V0, the number of microstep sequences of the A phase and the A bar phase is 8 times, and 8 times of the system clock. Cycle time (8
Tc) is the time of one step sequence. Further, the cycle of the one-phase step sequence is a time (16 · Tc) corresponding to 16 cycles of the system clock. Further, the A-bar phase is delayed from the A-phase by eight periods of the system clock.

By the way, the conveyance amount during recording one line of the color thermosensitive recording paper 1 by the conveyance roller pair 13 depends on the rotation speed of the capstan roller 13a, that is, the rotation speed of the first motor 15, and the rotation speed of the capstan roller 13a. Determined by the diameter. Although the capstan roller 13a is manufactured so that its diameter becomes a design value, it is actually slightly larger or smaller than the design value, but adjusting the diameter is practically impossible. Impossible. Therefore, a capstan roller having a diameter slightly larger than the designed value or a capstan roller having a smaller diameter is actually used.

When the diameter of the capstan roller 13a is different from the design value, the first motor 1 is driven at the same rotation speed.
Even if the roller 5 is rotated, the speed at which the color thermosensitive recording paper 1 is actually conveyed by the capstan roller 13a increases or decreases. That is, the transport amount in a fixed time for recording one line may be larger or smaller than the design value. For this reason, when the diameter of the capstan roller 13a is different from the design value, the cycle of the step sequence is increased or decreased by increasing or decreasing the number of microstep sequences in one step sequence according to the diameter of the capstan roller 13a. Adjust,
The transport speed Vp of the color thermosensitive recording paper 1 by the capstan roller 13a is set. In detail, by increasing or decreasing the number of micro-step sequences in one step sequence, the transport speed of the color thermosensitive recording paper 1 during recording of one line is adjusted. Thereby, the color thermosensitive recording paper 1 conveyed one line between recordings
Is adjusted to the designed value.

For example, the actual capstan roller 13a
Is smaller than the design value, a modified sequence data group in which the number of sequence data is reduced by the smaller value is used. FIG. 4 shows an example of this modified sequence data group. The modified sequence data group in FIG. 4 has contents in which the number of sequence data corresponding to the reference voltage V0 and the number of sequence data corresponding to the reference voltage V3 are reduced with respect to the standard sequence data group.

When this modified sequence data is used, the number of micro step sequences in one step sequence is six, and the cycle of the one-phase step sequence is 12 cycles of the system clock (12 · Tc).
Becomes In this way, by shortening the length of one step sequence and the cycle of the step sequence, the first step sequence can be compared with the case where the standard sequence data is used.
The rotation speed of the motor 15 is increased by the smaller diameter of the capstan roller 13a. In addition, the transport amount of the color thermal recording paper 1 during the recording of one line is designed.

Conversely, when the actual capstan roller becomes larger than the designed diameter, a modified sequence data group in which the number of sequence data is increased is used.
FIG. 5 shows an example of this modified sequence data group. FIG.
The corrected sequence data group has a content obtained by adding a total of four sequence data items corresponding to the reference voltage V1.
As a result, the number of micro-step sequences in one step sequence becomes ten, and the cycle of the one-phase step sequence becomes 20 cycles (2
0 · Tc). In this way, by increasing the length of one step sequence and the cycle of the step sequence, the rotation speed of the first motor 15 can be set to a smaller value than the case where the standard sequence data is used. Slow down by a large amount. In addition, the transport amount of the color thermal recording paper 1 during the recording of one line is designed.

As the ROM 50b, one in which a sequence data group based on the diameter of the capstan roller 13a measured at the time of manufacturing is written is used. The ROM 50b
Using an EEPROM as the capstan roller 1
A sequence data group based on the diameter of 3a may be written.

B-phase circuit 41b of first motor driver 41
Has a configuration similar to that of the A-phase circuit 41a.
The drive current is supplied to the B phase coil 18 and the B bar phase coil 19 of FIG. The number and contents of the sequence data of the sequence data group written in the ROM of the B-phase circuit 41b are the same as those of the A-phase circuit 41a. The address of each sequence data is determined so that the drive current is supplied to the B phase and the B bar phase with a delay by the cycle. FIG. 6 shows a standard sequence data group as an example of the sequence data group of the B-phase circuit 41b.

FIG. 7 shows the driving currents of the A-phase, A-bar phase, B-phase and B-bar phase when the standard sequence data group is used.
It shows a relationship between a system clock, a timing signal, and a sequence data value (hexadecimal number). In FIG. 7, the drive currents of the coils of the A-phase and the A-bar phase, and the B-phase and the B-bar phase are drawn together. For the A-bar phase and the B-bar phase, the driving current increases as the position becomes lower. When a drive current is flowing through the A phase, A
The drive current of the bar phase is “0”, the drive current of the A phase is “0” when the drive current is flowing through the A bar phase, and the same applies to the B phase and the B bar phase.

For example, from the A-phase circuit 41a to the A-phase coil 1
6 is synchronized with the system clock in response to the fact that each sequence data of the sequence data group of the ROM 50b is cyclically read from the address “0” and latched by the latch circuit 51. Therefore, the magnitude of the driving current is changed to I0, I at every time Tc.
0, I1, I2, I3, I3, I2, and I1 are supplied. In addition, the A-bar phase coil 17 has a drive current of I0, I0, I0 at a timing delayed from the A-phase by eight system clock cycles at every time Tc.
1, I2, I3, I3, I2, and I1. In this example, one step sequence increases the drive current stepwise from I0 to I3, and from I3 to I3.
This corresponds to a period in which it is reduced to one. One microstep sequence is a period of time Tc during which a constant drive current is supplied.

On the other hand, the phase of the B-phase coil 18 is delayed by 5 system clock periods from the A-phase, and the phase of the B bar-phase coil 19 is delayed by 8 system clock periods from the B phase. The size is I for each time Tc
Drive currents of 0, I0, I1, I2, I3, I3, I2, and I1 are supplied in order.

When the drive current of each phase is controlled using the standard sequence data group in this manner, the first motor 15 rotates its rotor 1 every eight periods of the system clock.
5a and one step angle θ determined by the structure of the stator. Also, during one step sequence,
The drive current supplied to each phase is changed stepwise by micro-step drive, and the rotation angle of the rotor is advanced little by little, so that the rotation of the rotor 15a can be reduced even during a short time for recording one line. Progress is smooth.

FIG. 8 shows the driving current of each phase according to the correction sequence data group of FIG. 4 corresponding to the case where the diameter of the capstan roller 13a is small. In this case,
The magnitude of the driving current of each phase is set to I0, I1, I
2, I3, I2, and I1. Therefore, the first motor 15 is output every six cycles of the system clock.
Is rotated by one step angle θ. FIG. 9 shows the drive current of each phase according to the correction sequence data group of FIG. 5 corresponding to the case where the diameter of the capstan roller 13a is large. In this case, the magnitudes of the driving currents of the respective phases become I0, I0, I1, I1, I2, I3,
I1, I2, I1, and I1 are supplied, and the first motor 15 is rotated by one step angle θ every ten periods of the system clock. In any of these cases, as in the case of the standard sequence data group, the rotor 15 can be moved within a short time for recording one line.
The rotation progress of a becomes smooth.

The second motor driver 42 and the third motor driver 43 have the same configuration as the first motor driver 41, but the capstan rollers 23 of the transport roller pairs 23, 33 in the corresponding print stages 20, 30, respectively.
Sequence data groups corresponding to the diameters of a and 33a are written. Thereby, each of the print stages 20, 30
The rotation speeds of the second and third motors are adjusted such that the color thermosensitive recording paper 1 is transported at the transport speed Vp.

Next, the operation of the above configuration will be described.
The color thermosensitive recording paper 1 from the recording paper roll is sent out to the transport path 3, and each of the print stages 10, 20, 3 is printed.
The respective thermal heads 12, 22, and 33 are moved to the pressure contact positions, and the heating element arrays 12a, 22a, and 3 are moved.
3 a is pressed against the color thermosensitive recording paper 1. The yellow light fixing device 14 and the magenta light fixing device 24 are lit.

On the other hand, the first to third motors 15, 25, 35
Are driven by the corresponding first to third motor drivers 41 to 43, respectively.
a, 23a and 33a are rotated. As a result, the color thermosensitive recording paper 1 nipped by the transport roller pairs 13, 23, and 33 is transported in the print stages 10, 20, and 30 from upstream to downstream.

For example, when the capstan roller 13a of the yellow print stage 10 has a designed diameter, the A-phase circuit 41a and the B-phase circuit 41b of the first motor / motor driver 41 use a standard sequence for each ROM. Since the data group has been written, the drive current shown in FIG. 7 is supplied to the coils 16 to 19 of each phase based on the timing of the system clock. As a result, the first motor 15 is rotated by one step angle θ every time (8 · Tc), and is rotated at a standard rotation speed according to the capstan roller 13a having the designed diameter.

Capstan roller 1 of transport roller pair 13
3a is rotated at the standard rotation speed of the first motor 15.
Therefore, since the linear velocity of the peripheral surface of the capstan roller 13a matches the designed transport speed Vp, the color thermosensitive recording paper 1 nipped by the transport roller pair 13 is moved at the transport speed Vp.
At p, the paper is continuously conveyed from the upstream to the downstream in the yellow print stage 10. During this transport, a yellow image is recorded by the heating element array 12a of the thermal head 12 for yellow one line at a time every four periods of the system clock.

The color thermosensitive recording paper 1 has a rotor 1 even if a short time for recording one line is viewed in a minute time width.
5a, that is, the rotation of the capstan roller 13a is smoothed and conveyed at a substantially constant conveyance speed Vp, so that the conveyance amount of the color thermosensitive recording paper 1 during recording of one line, that is, the yellow image The width of each line is
Each has a constant length (4 · Vp · Tc) determined by the transport speed Vp and the recording cycle (4 · Tc).

When the portion of the color thermosensitive recording paper 1 on which the yellow image is recorded is conveyed to the position of the yellow optical fixing device 14 by the conveying roller pair 13, the yellow thermosensitive recording material is irradiated with the ultraviolet light from the yellow optical fixing device 14. The color forming layer is light-fixed. Then, after the light fixing, the sheet is sent to the magenta print stage 20.

The color thermosensitive recording paper 1 entering the magenta print stage 20 is transported in the magenta print stage 20 by a pair of transport rollers 23 from upstream to downstream. If the diameter of the capstan roller 23a of the magenta print stage 20 is smaller than, for example, a design value, the second motor driver 42 based on the corrected sequence data group having smaller sequence data than the standard sequence data group by the smaller value. Drives the second motor 25. Therefore, in the second motor 25, the number of times of the micro step sequence in one step sequence is reduced, and the cycle of the step sequence is shortened. For example, a drive current as shown in FIG. Is driven.

As a result, the second motor 25 is rotated faster than the standard rotation speed by the smaller diameter of the capstan roller 23a, and the capstan roller 23a rotates at the same rotation speed as the second motor 25. As a result, the linear velocity of the peripheral surface of the capstan roller 23a matches the transport speed Vp, and the color thermosensitive recording paper 1 nipped by the transport roller pair 13 moves from the upstream to the downstream in the magenta print stage 20 at the transport speed Vp. It is conveyed continuously toward. During this conveyance, a magenta image is recorded line by line by the heating element array 22a of the magenta thermal head 22. The width of each line of the magenta image recorded on the magenta print stage 20 is the length (4 · Vp · Tc) as in the case of the yellow image.

When the portion of the color heat-sensitive recording paper 1 on which the magenta image is recorded reaches the position of the magenta light fixing device 24, ultraviolet light is irradiated from the magenta light fixing device 24, and the magenta heat-sensitive coloring layer is exposed to light. Be established. Then, after the light fixing, the sheet is sent to the cyan print stage 30.

In the cyan print stage 30, the color thermosensitive recording paper 1 is transported from the upstream to the downstream by the transport roller pair 33. Here, when the diameter of the capstan roller 33a of the transport roller pair 33 is, for example, larger than a design value, based on the corrected sequence data group in which the sequence data is larger than the standard sequence data group by the larger value, The third motor driver 43 drives the third motor 35. Therefore, the number of microstep sequences in one step sequence is increased, and the cycle of the step sequence is lengthened. For example, a drive current as shown in FIG. 9 is supplied to each phase coil.
The third motor 35 is driven.

As a result, the third motor 35 is rotated at a speed lower than the standard rotation speed by the larger diameter of the capstan roller 33a, and as a result, the linear velocity of the peripheral surface of the capstan roller 33a becomes equal to the transport speed Vp. 3 pairs of transport rollers
The color thermosensitive recording paper 1 nipped at 3 is continuously conveyed from the upstream to the downstream in the cyan print stage 30 at the conveying speed Vp, and the cyan image is line by line by the heating element array 32a of the cyan thermal head 32. Be recorded. Also in this case, the width of each line of the cyan image is the length (4 · Vp · Tc).

The portion of the color thermosensitive recording paper 1 on which the cyan image has been recorded is sent to a paper discharging mechanism by a pair of conveying rollers 33, and the paper is separated for each image by the paper discharging mechanism and then discharged. . In this manner, the color image recorded on the discharged color thermal recording paper 1 has the same line width for each color, and therefore no color misregistration or misregistration occurs.

In the above embodiment, the microstep driving is performed by setting the reference voltage to four levels. However, the number of microstep sequences in one step sequence is finely adjusted by using a multistep reference voltage. It is also possible to adjust the transport speed with higher accuracy. In the above embodiment, since the timing signal for starting the recording of one line is generated based on the system clock, the image is recorded line by line asynchronously with the rotation of the step motor. Alternatively, it may be of a synchronous type that generates a timing signal every time a fixed amount of color thermal recording paper is conveyed based on the number of executed step sequences.

There is also a one-head three-pass type thermal printer that records a color image in three color planes sequentially with one thermal head while reciprocating the color thermosensitive recording paper with a pair of conveying rollers. In the one-head three-pass type thermal printer, the thermal recording paper pressed by the thermal head is transported by being pulled by a transport roller pair.
Since an image is recorded during this time, the color thermosensitive recording paper is stretched. When elongation occurs, the actual transport speed, that is, the transport amount while one line is recorded, changes. The degree of the elongation changes depending on the coefficient of friction between the thermal head and the color thermosensitive recording paper, and the coefficient of friction changes with the temperature of the thermal head, that is, the color to be recorded. Therefore, the width of one line changes for each color to be recorded, which causes misregistration. Therefore, similarly to the above embodiment, if the motor is driven using a sequence data group that changes the cycle of the step sequence for each color to be printed,
Substantially the same conveyance speed during recording of each color can be made the same, and the width of one line of each color can be made the same to prevent misregistration.

In the above-described embodiment, the case where the thermal recording paper is conveyed by the thermal printer has been described. However, the recording paper or the web is conveyed by a plurality of capstan rollers, or the cord-like material is wound up. In such a case, the transport speed, the winding speed, and the like can be adjusted by the same driving method as above for various devices that need to adjust the transport speed, the winding speed, and the like of each capstan roller.

[0069]

As described above, according to the present invention, the stepping motor for rotating the capstan roller for transporting the recording paper is stepwise increased in drive current supplied to each phase and then stepwise. The micro-step drive for decreasing the number of micro-steps is performed.
The step speed is adjusted during each step motor by adjusting the cycle of the step sequence for each step motor, so that the recording paper transport speed by each capstan roller is the same. The transport amount for one line can be made the same, and the occurrence of color shift and registration shift can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a first motor driver that drives a first motor.

FIG. 2 is a schematic diagram showing a configuration of a three-head one-pass type color thermal print embodying the present invention.

FIG. 3 is an explanatory diagram showing a standard sequence data group for A phase.

FIG. 4 is an explanatory diagram showing an example of an A-phase correction sequence data group used when the diameter of a capstan roller is small.

FIG. 5 is an explanatory diagram showing an example of an A-phase correction sequence data group used when the diameter of a capstan roller is large.

FIG. 6 is an explanatory diagram showing a standard sequence data group for phase B.

FIG. 7 is a waveform chart showing a change in drive current when a standard sequence data group is used.

FIG. 8 is a waveform chart showing a change in drive current when the correction sequence data group of FIG. 4 is used.

FIG. 9 is a waveform chart showing a change in drive current when the correction sequence data group of FIG. 5 is used.

[Explanation of symbols]

 Reference Signs List 1 color thermal recording paper 12, 22, 32 thermal head 13, 23, 33 transport roller pair 13a, 23a, 33a capstan roller 15, 25, 35 motor 15a rotor 16-19 coil 41-43 motor driver 50 sequence data generation circuit

Claims (4)

[Claims] A plurality of recording heads for recording a specific color on recording paper line by line and a plurality of capstan rollers for transporting the recording paper are arranged along a transport path, respectively. A stepping motor is provided for each roller, and the recording paper is conveyed from the upstream side to the downstream side of the conveying path by rotating the corresponding capstan rollers with each of the stepping motors. In a printing method for recording a color image in a color plane sequence with a head for printing, a step sequence is periodically performed with a predetermined phase difference for each phase of the step motor, and a predetermined current is fixed in one step sequence. By performing a plurality of micro-step sequences that flow for a period of time, the drive current supplied to each phase is increased stepwise and then decreased stepwise, In addition to micro-step driving each step motor, the number of micro-step sequences in one step sequence is determined for each step motor according to the diameter of the corresponding capstan roller, and the cycle of the step sequence is adjusted. Wherein the recording paper transport speeds of the capstan rollers are matched with each other. 2. The thermal head according to claim 1, wherein the captan roller is provided for each of the thermal heads, and the thermal head records a specific color line by line while the recording paper is being conveyed by the corresponding captan roller. Item 7. The printing method according to Item 1. 3. A plurality of recording heads for recording a specific color on recording paper one line at a time, a plurality of capstan rollers for transporting the recording paper along a transport path, and a cap for rotating the capstan roller. A plurality of step motors are provided for each of the stun rollers, and the recording paper is conveyed from the upstream side to the downstream side of the conveyance path by rotating each of the corresponding capstan rollers with each of the step motors. In the printing apparatus, a color image is sequentially recorded in a color plane by each recording head, a step sequence is periodically performed with a predetermined phase difference for each phase of the step motor, and one step sequence is performed. By performing a plurality of microstep sequences in which a predetermined current is passed for a predetermined time, the drive current supplied to each phase is increased stepwise and then decreased stepwise. By driving each of the step motors, the number of micro step sequences in one step sequence is determined according to the diameter of the corresponding capstan roller, and the cycle of the step sequence is adjusted. Equipped with a motor driver for each step motor,
A printing apparatus, wherein the recording paper transport speeds of the capstan rollers are made equal to each other. 4. The thermal head according to claim 1, wherein the captan roller is provided for each of the thermal heads, and the thermal head records a specific color line by line while the recording paper is being conveyed by the corresponding captan roller. Item 3. The printing apparatus according to Item 3.