JP3500225B2 - Impact dot printer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes a print head which is vertically displaced according to the thickness of paper passing through a print gap formed between a platen and a print head at a vertically displaced position according to the paper thickness. The present invention relates to an impact dot printer that moves a print head to print on a print head with a constant print gap from the paper surface.

[0002]

2. Description of the Related Art In general, impact dot printers that print by impacting dot pins on paper positioned on a platen are often used when printing on bank passbooks or pressure-sensitive copy slips. . In a bank passbook, the paper thickness changes every time the page is turned, and in a copy slip, the paper thickness changes depending on the number of slips to be stacked. Therefore, in the impact dot printer, the print gap between the print head and the platen is adjusted according to such changes in the paper thickness, and printing is performed on the paper surface by the print head that is always at a constant distance from the paper surface on the platen. It is desirable to let them.

Impact dot printers have been known in the prior art in which the print head is displaced up and down in order to maintain a constant print gap between the print head and the paper. For example, in the printer disclosed in JP-A-3-97579, a contact type paper thickness sensor is provided on a carriage that supports a print head and moves horizontally on a carriage shaft. According to such a configuration, the paper thickness is always detected near the print head, so that a substantially constant print gap can be maintained even for paper with a non-uniform paper thickness, and as a result, good print results can be obtained. It becomes possible to obtain.

[0004]

However, in the printer disclosed in the above publication, the paper thickness sensor keeps in contact even when the print head moves in the horizontal direction during printing, so that the paper thickness sensor wears to cause the paper thickness sensor to wear. The reference point of the thickness sensor is misaligned, and the measured value of paper thickness tends to be inaccurate. Furthermore, since the paper thickness sensor is located right beside the print head, that is, on the horizontal movement trajectory of the printer head, in order to displace the print head up and down following the paper feed, the paper thickness should be measured at the same time. It is necessary to move the print head to a predetermined vertical displacement position according to the thickness. Therefore, even if the paper thickness of the paper part fed into the print gap suddenly becomes extremely large, the print head cannot be instantly raised according to the paper thickness, and the dot pin collides with the paper part and is damaged. I can't do it.

The present invention has been made in view of the above circumstances, and flexibly responds to changes in the paper thickness by measuring the paper thickness in advance before the print gap and continuously performing the measurement as the paper is fed. It is an object of the present invention to provide an impact dot printer that can perform.

Therefore, the present inventors propose to use a known non-contact type paper thickness sensor 101 as shown in FIG. 14 for gap adjustment of an impact dot printer. The non-contact type paper thickness sensor 101 includes a light emitting diode 102 that emits light L1 to the surface of the paper PP and a PS that detects reflected light L2 that is reflected while diffusing from the surface of the paper PP.
And a D (position sensitive detector) 103. As shown in FIG. 15, in the PSD 103, the position where the light intensity distribution of the reflected light L2 shows the maximum value (center of gravity position)
, And two current values I ₁ , depending on the position of the center of gravity,
Output I ₂ . Since the position of the center of gravity moves on the PSD 103 in proportion to the distance between the PSD 103 and the surface of the paper PP, the PSD 103 is detected by detecting the position of the center of gravity.
It is possible to measure the distance between the paper and the surface of the paper PP, that is, the paper thickness from the reference surface.

However, in such a PSD, since the measurement is carried out by using the light intensity distribution due to the diffusion of the reflected light, it shows good sensitivity to white paper, but to colored paper or paper with ruled lines. On the other hand, there was a problem that the measured values varied. The present inventors have completed the present invention in consideration of this point as well.

[0008]

To achieve the above object, according to a first aspect of the present invention, there is provided a print head which is vertically displaced in accordance with the thickness of paper passing through a print gap formed between the platen and the platen. , A paper feed pulse motor that feeds paper into the print gap for a specified length each time a phase drive pulse signal is applied, a pulse motor driver that outputs a phase drive pulse signal to the paper feed pulse motor, and a passage before the print gap. It is equipped with a paper thickness sensor that detects the paper thickness of the paper in synchronization with the phase drive pulse signal, and it is determined based on the detection result of the paper thickness sensor before the paper part whose paper thickness is detected in advance reaches the print gap. after moving the print head in the up and down displacement position, the line printing on the print head
An impact dot printer is provided which is characterized in that

According to a second aspect of the invention, in the impact dot printer according to the first aspect of the invention, the paper thickness sensor follows the contact with the paper surface and converts the size of the paper thickness into vertical displacement of the reflection surface. The paper thickness detection lever includes a thickness detection lever, a light emitting diode that emits light to the reflection surface, and a PSD that detects the distance to the reflection surface according to the light intensity of the reflected light reflected from the reflection surface. A supporting portion that is rotatably supported on a fixed base, a bending portion that is formed continuously with the supporting portion and that contacts the paper surface, and a white tape that is formed continuously with the bending portion and is attached It is characterized by including an amplifying section that constitutes a reflecting surface.

Further, according to a third aspect of the invention, in the impact dot printer according to the second aspect of the invention, the paper thickness sensor detects the position of the reflecting surface in the absence of the paper before the paper is taken into the print gap. The distance between the PSD and the reflecting surface is measured from the detection result, and the displacement of the reflecting surface according to the paper thickness is detected as the paper thickness based on the distance . Also, according to the present invention, based on the paper thickness of the detection result of the plurality of positions in the paper feeding direction of the paper, it is preferable to determine the vertical position of the print head. Further, according to the present invention, it is preferable to have a storage unit that stores the vertical displacement position of the print head determined based on the detection result of the paper thickness sensor.

According to the configuration of the first invention, the paper thickness sensor is
Since the paper thickness is measured in synchronization with the phase drive pulse signal of the paper feeding pulse motor, even if the paper thickness changes during the paper feeding, the print gap corresponding to the change can be established. Moreover, since the paper thickness is measured in advance before the print gap, it is possible to react to the change in the paper thickness in advance, and for example, the print head is adjusted to the print gap for subsequent printing before the line feed. It is also possible to do.

Further, according to the structure of the second invention, since the paper thickness detecting lever is attached to the fixed base rather than the carriage, the paper thickness detecting lever does not move due to the movement of the print head, and the lever of the lever does not move. Wear can be suppressed as much as possible. In addition, since the reflecting surface is composed of the white tape attached to the paper thickness detection lever, the accurate paper thickness can always be detected by the change of the paper color and the presence or absence of the ruled line even though the PSD is used. It will be possible.

Further, according to the third aspect of the invention, the sensor gap in the absence of the paper is measured before the paper is taken up to the print gap. Therefore, even if the paper thickness detection lever is lowered due to wear or the support mechanism of the paper thickness sensor is deformed and the sensor gap reference is deviated,
No error occurs in the sensor gap. Moreover, since this origin correction is performed every time a new paper is taken in, it is possible to always maintain an accurate reference of the sensor gap.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 schematically shows the overall structure of a horizontal paper feed type impact dot printer according to the present invention. The impact dot printer P includes a print head 10 that prints by impacting dot pins on paper. In this impact dot printer P, the paper is slid along the paper feed table 12 mounted on the front surface of the housing 11, and the paper is horizontally fed from the main paper feed port 13 to the print head 1.
Send to 0.

As shown in FIG. 2, the bottom plate 11a of the housing 11 has left and right frames 14 and 15 facing each other.
Is fixed. Between these left and right frames 14 and 15, a carriage shaft 17 that supports a carriage 16 on which the print head 10 is mounted so as to be horizontally movable.
Is passed. A platen 18 that receives the impact of the dot pin is arranged immediately below the locus of the print head 10 along the carriage shaft 17. Between the platen 18 and the tip of the print head 10, the main paper feed port 1
A print gap G through which the paper supplied from 3 and supplied for printing passes is defined. Print head 10
Prints on a sheet passing through the print gap G while moving horizontally along the carriage shaft 17 based on a control signal from a CPU (central processing unit) 19 mounted on the board on the bottom plate 11a. An ink ribbon (not shown) is attached to the carriage 16, and the ink ribbon is constantly supplied between the paper and the print head 10.

As is apparent from FIG. 3, a guide surface 21 for guiding the paper in the horizontal direction to the sub paper feed port 20 is connected to the main paper feed port 13. The print head 10 and the platen 18 face each other near the center of the guide surface 21. First and second paper feed roller means 22 and 23 for forcibly moving the paper fed to the guide surface 21 on the upstream side and the downstream side (viewing from the main paper feed port 13) across the platen 18. Is provided. The first and second paper feed roller means 22 and 23 are a pair of upper and lower cylindrical rollers 2.
The paper is fed by rotating the cylindrical rollers 26 and 27 while sandwiching the paper with 6 and 27.

Since the first and second paper feed means 22 and 23 have substantially the same structure, the first paper feed roller means 22 will be described in detail here as a representative. That is, referring to FIG. 4, the first paper feed roller means 22 is urged toward the lower cylindrical roller 26 and the lower cylindrical roller 26 that contacts the back surface of the paper at the same level as the guide surface 21. An upper cylinder roller 27 that sandwiches the paper with the lower cylinder roller 26 is provided. The upper cylindrical roller 27 rotates about a rotation shaft 31 which is swingably supported by a swing arm 30. The oscillating arm 30 urges the oscillating arm 30 to press the upper cylindrical roller 27 against the lower cylindrical roller 26. Therefore, the upper cylindrical roller 27 can arbitrarily change the gap with respect to the lower cylindrical roller 26, and as a result,
Even if the thickness of the paper passing between the upper and lower cylindrical rollers 27 and 26 changes, the change can be dealt with at any time.

Each cylindrical roller 26, 27 is connected to the frame 15
It is rotationally driven by the paper feed pulse motor 32 fixed to the. The driving force of the paper feed pulse motor 32 is transmitted to the cylindrical rollers 26 and 27 by a first driving force transmission mechanism 34 using a rubber belt 33. First driving force transmission mechanism 3
An endless rubber belt 33 is sequentially wound around the first idler 35, the first rotating pulley 36, the first transmitting pulley 37, the second idler 38, the second transmitting pulley 39, and the second rotating pulley 40 of No. 4. First and second rotating pulleys 36,
40 is fixed to the ends of the rotary shafts 41, 42 of the lower cylindrical rollers 26, 26 of the first and second paper feed roller means 22, 23. A transmission gear is coaxially fixed to the first and second transmission pulleys 37 and 39, and the transmission gears are the third and fourth fixed to the end portions of the rotating shafts 31 and 31 of the upper cylindrical rollers 27 and 27. The rotating gears 43 and 44 are rotated. Therefore, when the paper feed pulse motor 32 rotates the shaft clockwise, for example, the first and second rotary pulleys 36,
40 and the 1st and 2nd transmission pulleys 37 and 39 rotate clockwise, and the 1st and 2nd rotation gears 43 and 44 rotate counterclockwise. As a result, the upper cylindrical rollers 27, 27
And the paper is fed by the cooperation of the lower cylindrical rollers 26, 26. The rotation speed of the paper feed pulse motor 32 is CPU
It is set by the control signal from 19.

As is apparent from FIG. 5, the first and second
Adjacent to the paper feed roller means 22 and 23, three paper thickness sensors 50 for detecting the thickness of the paper passing through the print gap G are arranged. These three paper thickness sensors 50 are arranged so as to be displaced from each other in the width direction of the paper to be fed. Moreover, two are arranged on the upstream side of the platen 18 and one is arranged on the downstream side of the platen 18. The positions of these paper thickness sensors 50 may be arbitrarily set depending on the type of paper used for printing. For example, upstream 2
One paper thickness sensor 50 is effective when printing on a bank passbook in which the left and right paper thicknesses differ depending on the opened page.

As shown in FIG. 6, the paper thickness sensor 50 includes a reflection type photosensor 52 fixed / supported on the guide plate 51 above the guide surface 21, and a paper supported on the guide plate 51 so as to be swingable. And a thickness detection lever 53. For the reflection type photo sensor 52, refer to FIG.
Emits the light L1 to the reflection surface, and detects the distance from the reflection surface to the PSD 103 according to the light intensity of the reflected light L2 reflected from the reflection surface. The paper thickness detection lever 53 is a support portion 5 rotatably supported by a fixed guide plate 51 via a shaft 54.
3a and a bent portion 53b that is connected to the support portion 53a and traces the surface of the paper PP that passes through the print gap G.
An amplifying portion 53c which is formed continuously with the bent portion 53b and constitutes a reflecting surface by a white tape attached is provided. The light emitted from the light emitting diode is the paper thickness detection lever 53.
The light is reflected by the reflection surface on the upper surface of the amplification section 53c of the above and detected by the PSD. At this time, the paper thickness detecting lever 53 follows the surface of the paper PP and converts it into vertical displacement of the reflecting surface while amplifying the size of the paper thickness. The thickness of the paper PP passing through the print gap G can be detected by detecting the change in the distance from the state where the paper does not exist. Photo sensor 52
The distance signal corresponding to the paper thickness from the CPU is the control circuit
Sent to 19.

With reference to FIGS. 3 and 7, the gap adjusting device GG uses a signal from the CPU 19 based on the distance signal to move the print head 10 to the platen 18 according to the size of the paper thickness supplied. A printhead 1 that is closely / separated and has a constant distance from the paper surface on the platen 18.
Print gap G to print on paper at 0
Adjust. The gap adjusting device GG applies a driving force to the print head 10 via the second driving force transmission mechanism 60,
A print gap adjusting pulse motor 61 for moving the print head 10 close to / away from the platen 18 is provided. The CPU 19 controls the rotation amount of the pulse motor 61 based on the signal from the paper thickness sensor 50 according to the paper thickness.

The second driving force transmission mechanism 60 includes the frame 15
A displacement gear 62 is rotatably supported on. The carriage shaft 17 is eccentrically supported by the displacement gear 62. The two transmission gears 6 are attached to the sector gear 62a that concentrically extends from the rotation center of the displacement gear 62.
When the driving force from the pulse motor 61, which has been decelerated via 3 and 64, is applied, the displacement gear 62 rotates about the shaft 62b. For example, when the displacement gear 62 rotates clockwise in the drawing, the carriage shaft 17 descends, and thus the print head 10 also descends vertically. On the contrary, when the displacing gear 62 rotates counterclockwise in the drawing, the carriage shaft 17 rises, and therefore the print head 10 moves.
Also rises vertically.

A gap lever 65 as an abutment member is integrally connected to the displacement gear 62 of the second drive transmission mechanism 60. At the tip of the gap lever 65, a guide shaft 67 that passes through an arc-shaped guide hole 66 defined in the frame 15 is provided. The swing range of the gap lever 65 is restricted by one stopper plate 68. The stopper plate 68 is brought into contact with the gap lever 65 when the pulse motor 61 drives the print head 10 away from the platen 18 (indicated by a dashed line in the figure).
A first stopper 68a for restricting the displacement of the
The pulse motor 61 moves the print head 10 to the platen 18
And a second stopper 68b for restricting the displacement of the print head 10 in the proximity direction when the gap lever 65 comes into contact with the gap lever 65 when it is driven in the proximity direction. When the gap lever 65 comes into contact with the first stopper 68a, the pulse motor 61 tries to continue to rotate, and as a result, the pulse motor 61 loses synchronization, whereby the pulse motor 61 enters the initial state.
This initial state is determined as the reference position of the print head 10. From this initial state, the rotation amount of the pulse motor 61 is controlled based on the number of pulses, and the vertical displacement of the print head 10 according to the rotation amount is realized. The minimum print gap between the print head 10 and the platen 18 is determined by the gap lever 65 contacting the second stopper 68b. This minimum print gap matches the thinnest paper to be printed, eg
It is set to 0.3 mm.

FIG. 8 shows a schematic configuration of a print gap G adjusting circuit using the gap adjusting device GG. A first pulse motor driver 70 that outputs a phase drive pulse signal to the paper feed pulse motor 32 is supplied to the CPU 19 of the adjustment circuit.
And a second pulse motor driver 71 that outputs a phase drive pulse signal to the print gap adjusting pulse motor 61 are connected. A synchronous clock signal is supplied from the CPU 19 to the light emitting diodes of the first pulse motor driver 70 and the paper thickness sensor 50, and as a result, the paper feed pulse motor 32 sets the print gap G to the predetermined length each time the phase drive pulse is applied. At the same time as the paper is fed, the light emitting diode emits light, and the paper thickness sensor 50 detects the paper thickness for each phase drive pulse signal before the print gap G.

Further, the paper thickness sensor 50 and the photo interrupter 72 are connected to the CPU 19. The two currents output by the PSD of the paper thickness sensor 50 are converted into digital values by the A / D converter 73 according to the light intensity distribution of the reflected light, and C
It is taken into PU19. The photo interrupter 72 is
It is detected whether or not paper is present in the print gap G.

The average value calculation memory 74 is used for the paper thickness sensor 5
The measured value of the sensor gap (distance from the reflection surface to the PSD) detected by 0 is stored multiple times. The average value of the measured values is calculated based on the stored measured values. The origin data memory 75 stores the position of the reflecting surface in the absence of the paper, which is detected prior to taking in the paper up to the print gap G. Based on the sensor gap at this time, the displacement of the reflecting surface according to the paper thickness is detected as the paper thickness. The print gap position table 76 stores in advance optimum print gap positions (vertical displacement positions of the print head 10) for each expected paper thickness. That is, the CPU 19 as a head position adjusting circuit
Searches the optimum print gap position from the print gap position table 76 based on each detection result of the paper thickness sensor 50. The buffer 77 is, for example,
It is composed of a FIFO and sequentially stores print gap positions that are continuously searched as the paper is fed. The CPU 19 as a control circuit reads the corresponding print gap position from the buffer 77 when the paper portion whose paper thickness is detected by the paper thickness sensor 50 is fed into the print gap G.

Next, the operation of this embodiment will be described with reference to the flowchart of FIG. When the impact dot printer P is powered on in the first step S1, the origin correction of the paper thickness sensor 50 is performed in the second step S2. By this origin correction, the reference position of the sensor gap is set. Subsequently, in a third step S3, the print gap adjusting pulse motor 61 once raises the print head 10 to the maximum extent, and the stepping of the pulse motor 61 sets the print gap position reference position. An accurate print gap position is defined according to this reference position. At this point, the preparation for printing is completed, and the impact dot printer P enters the standby state (fourth step S
4) Wait for print command input.

When the CPU 19 receives the print command in the fifth step S5, the impact dot printer P
The paper feed table 1 is operated by operating the paper feed pulse motor 32.
Take in paper from 2. In the sixth step S6, first, the first line printing process is performed on the loaded paper in accordance with the received print command. If there is a subsequent print command at the time when the printing of the first line is completed, the subsequent continuous print processing is further performed on the same paper (seventh and eighth steps S7 and S8). Ninth step S9
When it is detected that the printing of one page has been completed, the paper is discharged from the sub paper feed port 20 in the tenth step S10, and the origin correction is performed again when the paper passes through the print gap (the eleventh step S11). . If a print command is further input, the second page of paper is taken in and the sixth step S6
The processing from the 11th step S11 is repeated. If there is no print command, the process directly returns to the standby state of the fourth step S4 and waits for the next print command. If there is no subsequent print command when the printing of the first line is completed, the process proceeds from the seventh step to the tenth step S10 to eject the paper.

If the power of the impact dot printer P is turned off while the impact dot printer P is in the standby state, the operation of the impact dot printer P is completed.

The sensor gap origin correction processing in the second step S2 and the eleventh step S11 of FIG. 9 is shown in FIG.
Further details will be given with reference to 0. In this origin correction process, in the first step Q1, the photo interrupter 72 detects whether or not paper is present in the print gap G. If there is paper, the process proceeds to the second step Q2 and the origin data stored in the origin data memory 75, that is,
Keep the value of the sensor gap as it is without paper. The origin data memory 75 stores origin data measured in advance from the time of factory shipment.

When it is determined that there is no paper in the first step Q1, the origin data is read from the origin data memory 75 to the CPU 19 in the third step Q3. Subsequently, the sensor gap is measured N times, for example, four times using the paper thickness sensor 50 (fourth and fifth steps Q4 and Q5).
Each time the measurement is performed, the measured value is stored in the average value calculation memory 74. When N measurements have been completed, the sixth step Q
At 6, the CPU 19 reads the measured value N times from the average value calculation memory 74 and calculates the average value. The calculated average value is compared with the origin data read in the third step Q3 (seventh step Q7). At this time, if the average value is within the predetermined allowable range (± α) with respect to the origin data, the process proceeds to the second step Q2 and the origin data is maintained as it is. This processing eliminates the need for the CPU 19 to frequently rewrite the origin data. If the average value has changed beyond the allowable range, the process proceeds to the eighth step Q8, and the CPU 19 rewrites the contents of the origin data memory 75 and stores the average value as the origin data.

According to such origin correction, the sensor gap without a paper is always measured before the paper is taken in up to the print gap. Therefore, the paper thickness detection lever 53 moves down due to wear, and the paper thickness sensor 5
Even if the support mechanism of 0 is deformed and the reference of the sensor gap is deviated, an error does not occur in the sensor gap.
Moreover, since this origin correction is performed every time a new paper is taken in, it is possible to always maintain an accurate reference of the sensor gap.

The first line printing process in the sixth step S6 of FIG. 9 will be described in more detail with reference to FIG. In the first step T1, the number of sensor gap measurements is set to N = 1. Paper feeding is started in the second step T2, and the impact dot printer P takes in paper from the main paper feeding port 13. At this time, a signal synchronized with the clock signal to the first pulse motor driver 70 that takes in the paper is input from the CPU 19 to the paper thickness sensor 50, and the paper thickness sensor 50 receives each phase drive pulse signal of the paper feed pulse motor 32. Measure the sensor gap. Therefore, by applying one phase drive pulse signal, the paper is fed into the print gap by a predetermined length, for example, 1/360 inch, and at the same time, the paper thickness sensor 50 detects the sensor gap once (third step T3). As a result, the paper thickness sensor 50 continuously detects the paper thickness while the paper is being fed to the print gap.

In the fourth step T4, it is determined whether or not the measurement of the sensor gap is the fourth time. If the number of measurements is less than 4, the process proceeds to the fifth step T5, and the measured value is stored in the average value calculation memory 74. Sixth step T6
If it is determined that the paper has not reached the print start position, the process returns to the third step T3 again, and the sensor gap is measured every 1/360 inch.

When it is determined in the fourth step T4 that the measurement of the sensor gap is the fourth time, the CPU 19 reads the measurement value stored in the average value calculation memory 74 and calculates the average value of the four measurement values. (7th step T7). The obtained average value is used as the origin data memory 7 by the CPU 19.
The data is compared with the origin data stored in memory 5 and the difference therebetween is obtained (eighth step T8). Then, the CPU 19 searches for the print gap position from the print gap position table 76 in the ninth step T9 based on the obtained difference. The retrieved print gap positions are sequentially stored in the buffer 77 in the tenth step T10.

As is clear from the branch of the sixth step T6, the processing from the third step T3 to the tenth step T10 is repeated until the paper reaches the print start position. That is, each time the 1/360 inch paper advances, the paper thickness sensor 50 detects the sensor gap, and the print gap position is sequentially written every time four measurements are completed.

When the paper reaches the print start position, the paper feeding is stopped. Then, in an eleventh step T11, the print gap position traced back a predetermined number of times is read from the buffer 77. That is, since the paper thickness sensor detects the paper thickness before the print gap, the print gap position corresponding to the detected paper thickness is temporarily stored in the buffer 77 until the paper is fed and reaches the print gap. It Here, the number of measurements stored in the buffer 77, that is, the number of measurements to be traced back is determined by the number of phase drive pulses required to feed the paper for the distance from the paper thickness sensor 50 to the print gap G. It The CPU 19 reads the corresponding print gap position from the buffer 77 when the paper portion whose paper thickness is detected by the paper thickness sensor 50 is fed into the print gap G. In the twelfth step T12, the vertical position of the print head 10 is adjusted based on the read print gap position. The print head 10 prints the first line according to the adjusted print gap position.

Next, the post-continuation printing process in the eighth step S8 of FIG. 9 will be described in more detail with reference to FIG.
First, in the first step U1, the current number of measurements is set.
At this time, the number of measurements used is the one that has continued from the previous processing. In the second step U2, the print gap position corresponding to the next print line is read from the buffer 77 before the paper is fed after printing. In the third step U3,
The vertical position of the print head 10 is adjusted based on the read print gap position. After this adjustment,
Based on the print command, n / 360 inch line feed is started (fourth step U4). In this way, since the vertical position of the print head 10 is adjusted prior to the paper feeding,
Before the paper unit is fed into the print gap G, the print gap position corresponding to the paper thickness is established in advance. As a result, it is possible to prevent the dot pins of the print head 10 from coming into contact with the paper even if the paper thickness is significantly increased.

When the paper feed is started, the sensor gap is measured every 1/360 inch (fifth step U5). In the sixth step U6, it is determined whether or not the measurement of the sensor gap is the fourth time. If the number of measurements is less than 4, the process proceeds to the seventh step U7, and the measured value is stored in the average value calculation memory 74. If it is determined in the eighth step U8 that the paper feed of n / 360 inches has not been completed, the process returns to the fifth step U5 again, and the sensor gap is measured every 1/360 inch.

When it is determined in the sixth step U6 that the measurement of the sensor gap is the fourth time, the CPU 19 reads out the measurement value stored in the average value calculation memory 74 and calculates the average value of the four measurement values. (9th step U9). The obtained average value is used as the origin data memory 7 by the CPU 19.
It is compared with the origin data stored in the 5th memory and the difference therebetween is obtained (tenth step U10). Subsequently, the CPU 19
Based on the obtained difference, the print gap position table 76 is searched for the print gap position in the eleventh step U11. The retrieved print gap positions are sequentially buffered in the twelfth step U12.
Stored in 7.

When it is judged in the eighth step U8 that the paper feeding is completed, one line is printed in the thirteenth step U13. Fifth step U5 to twelfth step U
The processes up to 12 are repeated until the paper feeding is completed.
That is, each time the 1/360 inch paper advances, the paper thickness sensor 50 detects the sensor gap, and the print gap position is sequentially written every time four measurements are completed.

According to the above printing process, the paper thickness sensor 50 measures the paper thickness in synchronization with the phase drive pulse signal of the paper feed pulse motor 32, so that the paper thickness changes during the paper feed. The print gap G corresponding to the change can be established. Moreover, since the paper thickness is measured in advance before the print gap G, it is possible to react swiftly to the change in the paper thickness, and the print head 1 is placed in the print gap G for printing which precedes before the inter-sheet feeding.
It is also possible to adjust 0. In addition, since the average value of the sensor gap is used to search for the print gap position, it is possible to obtain the optimum print gap position while suppressing variations in the measured values due to sensor characteristics and the like.

FIG. 13 is a flow chart showing how the paper thickness sensor 50 detects the sensor gap.
Referring also to FIG. 14, first, in the first step V1, C
Light emitting diode 1 according to the light emission control signal from PU19
02 is emitted. The emitted light L1 is the paper thickness detection lever 5
Reflected on the white tape of No. 3, the reflected light L2 is PSD10
Light is received at 3. Two currents I ₁ and I ₂ are output from the PSD 103 according to the logic of FIG. The voltages V ₁ and V ₂ corresponding to the output current are respectively A / D converter 73
Is converted into digital values V ₁₀ and V ₂₀ (second and third steps V2 and V3). In the fourth step V4, the light emitting diode 102 is turned off. Two voltage values V _1OFF from PSD103 when off, reads the V _2off (fifth, sixth step V5, V6), the difference VU between the voltage value at the time of emission
1, VU2 is calculated (7th and 8th steps V7, V
8). In the ninth step V9, the calculated current values VU1, VU
The sensor gap is calculated from U2 according to a predetermined formula.
Each constant is for ensuring the linearity between the sensor gap and the current value. The sensor gap calculated in the tenth step V10 is written.

In the above embodiment, the number of measurements when obtaining the average value of the measured values of the sensor gap can be set arbitrarily. In addition, the printing process performed at one time may print not only one line but a plurality of lines at once.

[0046]

As described above, according to the first aspect of the invention, the paper thickness is measured in advance before the print gap, and the measurement is continuously performed according to the paper feed, so that the change in the paper thickness can be flexibly dealt with. In addition, the vertical displacement control of the print head can be surely performed.

According to the second aspect of the invention, since the paper thickness detecting lever is attached to the fixed base instead of the carriage, the paper thickness detecting lever does not move due to the movement of the print head, and the lever is not worn. It can be suppressed as much as possible. Moreover, despite using PSD,
Since the reflecting surface is composed of the white tape attached to the paper thickness detection lever, it is possible to always detect the accurate paper thickness even if the paper color changes and the presence or absence of ruled lines.

Further, according to the third aspect of the invention, the sensor gap in the absence of the paper is measured before the paper is taken into the print gap. Therefore, even if the reference of the sensor gap is deviated due to the lowering of the paper thickness detection lever due to wear or the deformation of the support mechanism of the paper thickness sensor, no error occurs in the sensor gap. Moreover, since this origin correction is performed every time a new paper is taken in, it is possible to always maintain an accurate reference of the sensor gap.

[Brief description of drawings]

FIG. 1 is a schematic front view showing an entire horizontal paper feed type impact dot printer according to the present invention.

FIG. 2 is a schematic front view showing a frame set in the printer.

3 is a schematic cross-sectional view taken along line 3-3 of FIG. 1, showing a main part of a drive mechanism of the printer.

FIG. 4 is an enlarged schematic view showing a drive mechanism of paper feed roller means of the printer.

FIG. 5 is a cross-sectional plan view schematically showing a main part of a drive mechanism of the printer.

FIG. 6 is a diagram schematically showing a paper thickness sensor.

FIG. 7 is a diagram showing a main part of a gap adjusting device.

FIG. 8 is a block diagram showing a print gap adjusting circuit.

FIG. 9 is a flowchart illustrating the overall processing of the printer.

FIG. 10 is a flowchart illustrating a sensor gap origin correction process.

FIG. 11 is a flowchart illustrating first line printing processing.

FIG. 12 is a flowchart illustrating a post-continuation printing process.

FIG. 13 is a flowchart illustrating data processing from the paper thickness sensor.

FIG. 14 is a diagram showing a circuit configuration of a known non-contact type paper thickness sensor.

FIG. 15 is a diagram showing the operating principle of the PSD of the paper thickness sensor.

[Explanation of symbols]

G print gap, PP paper, 10 print head, 18 platen, 19 CPU as head position adjustment circuit and control circuit, 32 paper feed pulse motor, 50 paper thickness sensor, 53 paper thickness detection lever, 53a
Support part, 53b bending part, 53c amplifying part, 70 pulse motor driver, 77 buffer, 102 light emitting diode, 103 PSD.

─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kozo Abe 6-1-12 Honmachi, Tanashi City, Tokyo Citizen Watch Co., Ltd. Tanashi Factory (72) Inventor Takeya Uehara 6-1-12 Honmachi, Tanashi City, Tokyo Citizen Watch Co., Ltd. Tanashi Factory (56) Reference JP-A-4-1072 (JP, A) JP-A-5-169762 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B41J 25/308

Claims (5)

(57) [Claims] 1. A print head that is vertically displaced according to a paper thickness of a paper passing through a print gap formed between a platen, and a paper that feeds the paper into a print gap of a predetermined length each time a phase drive pulse signal is applied. A feed pulse motor, a pulse motor driver that outputs a phase drive pulse signal to the paper feed pulse motor, and a paper thickness sensor that detects the paper thickness of the paper passing in front of the print gap in synchronization with the phase drive pulse signal. Before moving the print head to the vertical displacement position determined based on the detection result of the paper thickness sensor before the paper part whose paper thickness is detected reaches the print gap, print on the print head. impact dot printer, characterized in that cause I. 2. The impact dot printer according to claim 1, wherein the paper thickness sensor follows and contacts the paper surface and converts the size of the paper thickness into vertical displacement of the reflection surface, and a reflection surface. A light emitting diode that emits light and a PSD that detects the distance to the reflecting surface according to the light intensity of the reflected light reflected from the reflecting surface are provided, and the paper thickness detection lever rotates on a fixed base. A supporting portion that is freely supported, a bending portion that is formed continuously with the supporting portion and that contacts the paper surface, and an amplification portion that is formed continuously with the bending portion and that constitutes the reflecting surface by a white tape attached An impact dot printer comprising: 3. The impact dot printer according to claim 2, wherein the paper thickness sensor detects the position of the reflection surface in the absence of paper before the paper is taken into the print gap.
An impact dot printer characterized in that the distance between the PSD and the reflection surface is measured from the detection result, and the displacement of the reflection surface according to the paper thickness is detected as the paper thickness based on the distance. 4. The impact dot printer according to claim 1, wherein the vertical position of the print head is determined based on the detection result of the paper thickness at a plurality of positions in the paper feeding direction. 5. The impact dot printer according to claim 1, further comprising a storage unit that stores the vertical displacement position of the print head determined based on the detection result of the paper thickness sensor.