Driving mechanism for head

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to, for example, a drive mechanism for a write head used in a printer or the like.

【0002】

[Conventional technology]

Conventionally, optical printers using a phosphor head, an LED head, or the like have linearly moved the print head to write light on photosensitive paper. Further, in inkjet printers and thermal printers, the printer head is moved linearly with respect to the recording paper for recording.

【0003】

FIG. 7 is a perspective view showing an example of an outline of configuring the head drive mechanism of such a printer, and FIG. 8 is a schematic view showing a part of a transmission system in which the head is moved by a wire rope. In FIG. 7, the front portion of the printer housing 51 is partially cut off, and two guide shafts 53 are fixed to the housing 51 at both ends via a gantry 52. The base 63 is slidably supported by the guide shaft 53 by two bearings 54 formed at both ends. Although not shown, the photosensitive paper can be set on the upper surface of the housing 51 with the photosensitive paper facing down.

【0004】

The photosensitive head 64 is mounted on the base 63, and the photosensitive head 64 is configured as an optical writing module. A dot block 64a for light writing is formed on the photosensitive surface of the photosensitive paper, and a plurality of light emitting dots forming recording dots are arranged in a staggered pattern on the dot block 64a. Each of the light emitting dots emits light with a brightness corresponding to a drive signal supplied from a drive signal generation unit (not shown).

【0005】

The photosensitive head 64 moves at a predetermined speed along the guide shaft 53 by a transmission system described later. When the moving speed fluctuates, for example, periodically due to the mechanical accuracy of the power drive system, Color unevenness may occur in the image exposed by the photosensitive head 64. Therefore, the applicant first described the occurrence of color unevenness due to the fluctuation of the moving speed of the photosensitive head 64 by the interval (Ds) of the light emitting dot trains arranged in a staggered pattern and the reduction ratio of the drive system that moves the photosensitive head 64. A method of suppressing by choosing the relationship appropriately was proposed as Japanese Patent Application No. 8-67523.

【0006】

FIG. 8 shows the drive system of the above application. The motor 56 is attached to the motor mounting plate 55 fixed to the housing 51 of FIG. 7, and the drive pulley 57 is fixed to the output shaft 56a thereof. Further, the tension adjusting lever 61 is attached to the pulley mounting base 60 fixed to the housing 51. A wire rope 58 is hung on the drive pulley 57 and the driven pulley 59, and both ends are crimped with a metal fitting 58a to make it endless. The wire rope 58 is fixed to the base 63 at the metal fitting 58a, and the photosensitive head 64 mounted on the base 63 is fixed so as to move in conjunction with the wire rope 58. In reality, the wire rope 58 is wound around the drive pulley 57 a plurality of times to prevent slippage between the pulley and the wire rope.

【0007】

A shaft 61a is fixed to one end of the tension adjusting lever 61, and the shaft 61a is swingably supported by a pulley mounting base 60. A support shaft 61c is crimped to the center of the tension adjusting lever 61 to rotatably support the pulley 59. The spring 61b is hooked on the hole formed at the other end of the tension adjusting lever 61, and the other end of the spring 61b is hooked on the tip of the tension adjusting screw 62 to rotate the tension adjusting screw 62 to apply the tension of the wire rope 58. It can be adjusted.

【0008】

When the motor 56 rotates, the rotational force rotates the drive pulley 57 via a reduction gear (not shown), and the rotational force transfers the base 63 to the guide shaft 53 via the drive pulley 57 and the wire rope 58. Along with sliding in the direction of the arrow in FIG. 7, the photosensitive head 64 on the base 63 also slides in the direction of the arrow, that is, in the scanning direction of the head. Since this drive system uses a wire drive system using a drive pulley 57 and a wire rope 58 in the final stage of the power transmission system for moving the head in the scanning direction, the reduction gear and the rotation unevenness of the pulley 57 are eliminated. , The head can be moved at a uniform speed.

【0009】

[Problems to be Solved by the Invention]

However, the wire drive for smooth power transmission also has the following problems. It is necessary to crimp the end of the wire rope to make it endless, and as mentioned above, in order to counter slip, the wire rope must be wound around the drive pulley during assembly, resulting in poor workability. .. Further, if the diameter of the drive pulley is reduced in order to reduce the size of the printer, a thin wire must be used due to the limitation of the allowable bending radius of the wire, and the wire is easily caught by an object and bent, further lowering the workability. Furthermore, nylon coating is required for the wire rope to ensure the life of the pulley, but since great care is taken not to damage the coating during assembly, it also contributes to the deterioration of workability. There is.

【0010】

Further, when the target printer is portable, the photosensitive head is also used in a vertically up-and-down posture, so that the load increases as compared with the horizontal movement, and slip between the drive pulley and the wire rope is likely to occur. As a countermeasure, it is necessary to increase the output by changing to a large motor, increase the tension of the wire rope, and increase the number of times the wire rope is wound around the drive pulley to increase the slip torque, but the cost will increase and the assembly man-hours will increase. Both of them lead to an increase in manufacturing cost, which is not preferable.

【0011】

Therefore, it is conceivable to use a toothed belt (commonly known as a timing belt) that is generally used in precision small machines, but there is another problem with the ultra-small toothed belt that can be used in such printers. Occurs. That is, when the toothed belt moves, a slow speed (speed unevenness) of the toothed belt may occur in which the time required to move the distance corresponding to the distance (pitch) between adjacent teeth is a cycle. This phenomenon is considered to occur especially due to the flexibility of the toothed belt.

【0012】

FIG. 9 is a schematic view of a toothed pulley 71 on the driving side and a toothed belt 70 that is hung and driven by the pulley 71. The toothed belt 70 is a flat belt with teeth 70a formed at regular pitches P. The flat belt and teeth are made integrally to maintain tensile strength and to keep the belt extension within the standard. In addition, a body such as glass fiber is kneaded into the flat belt part. Further, since it is used by wrapping it around a toothed pulley, it has appropriate flexibility. When the toothed pulley 71 transmits rotation to the toothed belt 70, normally, the side surfaces of the tooth 70a and the tooth 71a of the toothed pulley 71 come into contact with each other, and the rotation is transmitted by the teeth. The inside 70b of the flat belt portion of the toothed belt 70 hits the arc portion of the tooth tip, and the rotation is transmitted even by the friction of this portion. Further, the thickness of the teeth of the belt and the pulley is made relatively thin, and when the belt is hung on the pulley, the gap between the teeth is also relatively large.

【0013】

In addition, in order to prevent the belt from vibrating during operation and to fit the belt to the pulley, it is preferable to apply initial tension to the belt in advance when the belt is stopped, but in order to reduce the loss that occurs during transmission. , Very small toothed belts are often used without giving sufficient initial tension. Therefore, the flat belt part and the tooth part are not completely bent in an arc shape and fit into the toothed pulley 71 as in the part A in FIG. 9, but the thin flat belt part is like B. It bends in the shape of a C, and the tooth part tends to remain flat like C. In the former, the toothed belt 70 is longer than the arc of the corresponding toothed pulley 71, and in the latter, the toothed belt 70 is shorter. Therefore, even if the toothed pulley 71 rotates at a constant speed, the toothed belt 70 causes a slow speed with respect to the average speed, and this speed unevenness occurs repeatedly for each tooth, causing color unevenness in the printed image. Attract.

【0014】

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention has a plurality of recording dots arranged at predetermined intervals, and the recording dots do not overlap each other in the scanning direction of the recording medium. From the head having a writing block in which a plurality of recording dot trains arranged in such a manner are arranged with an interval Ds, a driving unit for driving the head relative to a recording medium, and the driving unit. In a head drive mechanism having a transmission system for transmitting power to the head and the final transmission system of the transmission system composed of a toothed pulley and a toothed belt, the toothed belt is converted into a relative movement distance of the head. The tooth pitch is 2Ds / (2n + 1) However, n is 0 or a positive integer It is configured to be.

【0015】

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment using the drive mechanism of the printer head of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view of the printer, and FIG. 2 is an enlarged perspective view of the toothed belt portion of the drive mechanism. In FIG. 1, the front portion of the printer housing 1 is partially cut off, and two guide shafts 3 are fixed to the housing 1 at both ends via a gantry 2 inside. The base 13 is slidably supported by the guide shaft 3 by two bearings 4 formed at both ends. Although not shown, a photosensitive paper with the photosensitive surface facing down is installed on the upper part of the housing 1 in FIG. 1, and an image can be exposed and printed by a photosensitive head 14 described later.

【0016】

The photosensitive head 14, which is configured as an optical writing module, is mounted on the base 13. The photosensitive head 14 is formed with a dot block 14a for light writing on the photosensitive surface of the photosensitive paper. In this dot block 14a, as will be described later, a plurality of light emitting dots forming recording dots are arranged in a staggered pattern. Each light emitting dot emits light one line at a time with a brightness corresponding to a drive signal supplied from a drive signal generation unit (not shown).

【0017】

Explaining the details of the drive system with reference to FIG. 2, a motor 6 having a built-in reduction mechanism is attached to a motor mounting plate 5 fixed to the housing 1, and a toothed pulley 7 for driving is attached to the output shaft 6a. Is fixed. The tension adjusting lever 11 is attached to the toothed pulley mounting base 10 which is also fixed to the housing 1. A toothed belt 8 is hung on the toothed pulley 7 on the driving side and the toothed pulley 9 on the driven side. Since this toothed belt 8 is fixed to the base 13 at one place by the fixing plate 13a and the screw 13b, the photosensitive head 14 mounted on the base 13 has exactly the same speed as the toothed belt 8. Exercise. Since the motor 6 usually has a built-in gear mechanism for deceleration, in this example, the toothed belt and the toothed pulley form the final transmission stage.

【0018】

For example, the tension adjusting lever 11 has a shaft 11a fixed to one end thereof, and the shaft 11a is swingably supported by a toothed pulley mounting base 10. Then, the support shaft 11c is crimped to the central portion of the tension adjusting lever 11 to rotatably support the pulley 9. A spring 11b is hooked on a hole formed at the other end of the tension adjusting lever 11, and the other end of the spring 11b is hooked on the tip of the tension adjusting screw 12 to rotate the tension adjusting screw 12 to rotate a toothed belt. It suffices to be able to adjust the tension of 8. When the motor 6 rotates, the base 13 slides along the guide shaft 3 in the direction of the arrow in the figure via the toothed pulley 7 and the toothed pulley 8 on the drive side. The photosensitive head 14 on the base 13 also slides in the direction of the arrow, that is, in the scanning direction of the head.

【0019】

As described above, even if the toothed pulley 7 makes a constant velocity circular motion, periodic speed unevenness occurs in the toothed belt 8, and this speed unevenness is repeated at a cycle corresponding to the tooth pitch of the toothed belt 8. appear. As described above, since the toothed belt 8 and the photosensitive head 14 move in exactly the same manner, the photosensitive head 14 also has a velocity unevenness with a period corresponding to the tooth pitch, and the printed image corresponds to the tooth pitch. Periodic color unevenness may occur.

【0020】

The color unevenness caused by the speed unevenness will be described below. FIG. 3 (a) schematically shows a part of the dot block 14a formed on the photosensitive head 14 and exposing the photosensitive paper. The dot block 14a is a line A consisting of light emitting dots Dt0, Dt2, Dt4 ... Consists of even dots, and a row B consisting of light emitting dots Dt1, Dt3, Dt5 ... Consists of odd dots. It forms a group of light emitting dots composed of lines. Furthermore, in columns A and B, the emission dots are arranged in a staggered pattern with an interval of Ds. Then, by sliding the photosensitive head 14 by the drive system as shown in FIG. 1, the photosensitive surface is scanned in the direction of the arrow, and one row of images is scanned in the main scanning direction of the photographic paper by rows A and B. Is sequentially exposed to.

【0021】

FIG. 3 (b) shows the exposed photosensitive paper surface. For example, in the X column, the emission dots in the A column first expose the 0, 2, 4, 6, and 8 squares, and the photosensitive head 14 slides at intervals Ds. After a period of movement, the emission dots in row B expose the squares 1, 3, 5, and 7. This completes the exposure of column X. Since each light emitting dot emits light according to a drive signal supplied from a light emitting dot drive unit (not shown), for example, the light emitting dot Dt0 is 0 in the X column, 0 in the X + 1 column, 0 in the X + 2 column, and X. Exposed as 0 ... in +3 row, the emission dot Dt1 is delayed by the time corresponding to the interval Ds, 1 in X row, 1 in X + 1 row, 1 in X + 2 row, 1 in X + 3 row. ... and expose.

【0022】

If the sliding speed of the photosensitive head 14 is uneven and a periodic slow speed occurs, the exposed image becomes darker when the moving speed of the photosensitive head 14 is slower than the average speed, and the exposed image becomes darker when the moving speed of the photosensitive head 14 is faster than the average speed. Becomes thinner. In other words, as shown in Fig. 4, when the period converted to the movement distance of the head with uneven speed is close to the distance Ds between columns A and B, for example, the light emitting dots in column A in column X If the head movement speed is slow when exposing with, the squares of 0, 2, 4, 6, and 8 will be dark, and then when exposing to the X column with the light emitting dots of the B column, if the movement speed is slow, 1, 3 By darkening the squares of, 5 and 7, all the X columns are exposed deeply. In this example, when the X column is dark, the X + 1 column is thin, and the X + 2 column is dark, shades appear every other column, and color unevenness or brightness unevenness appears remarkably.

【0023】

Therefore, the present invention reduces the color unevenness by setting the speed unevenness so as to have an appropriate period, and an example thereof will be described with reference to FIG. As shown in this figure, the period of velocity unevenness is set to be half a period with respect to the interval Ds between columns A and B. Then, when the shades of columns A and B are entered in the same way as in Fig. 4, the shades appear alternately in columns X, X + 1, and X + 2 as shown in Fig. 4 (b). As a result, the entire screen is aligned to the same density. FIG. 6 shows the relationship between the period of velocity unevenness in which color unevenness does not occur in the exposed image and the interval Ds between columns A and B. Assuming that the interval between the dots in columns A and B is Ds in Fig. 6, the velocity unevenness should be an odd multiple of one cycle (2π) (represented by Q) within twice this interval Ds. You can see that. If the speed unevenness of one cycle is exactly the same as the moving speed of the photosensitive head and the toothed belt as shown in FIG. 1, the cycle Q of FIG. 6 is the interval P of the toothed belt of FIG. 9, that is, the toothed pulley. Corresponds to the tooth pitch. Therefore, the relative movement distance obtained by converting the pitch of one tooth of the gear of the transmission system into the movement amount of the photosensitive head is 2Ds / (2n + 1) However, n is 0 or a positive integer The transmission system should be created so that

【0024】

In the case of the printer described as the above embodiment, the distance Ds between the light emitting dots A row and the B row of the photosensitive head 14 is 0.5 mm, and the tooth pitch of the toothed belt 8 is 1 mm. In this example, the relative movement distance described above is exactly the same as the movement speed of the photosensitive head and the toothed belt, so 1 mm of the tooth pitch can be used as it is, when n in (2n + 1) in the previous equation is 0. Correspondingly, it was possible to almost eliminate the occurrence of color unevenness in the exposed image. In this example, the reduction ratio of the reduction mechanism built into the motor is approximately 34, the number of teeth of the toothed pulley is 34, and the period of speed unevenness generated by the eccentricity of the toothed pulley itself is long, so that it is hardly affected.

【0025】

If the effect of speed unevenness of the speed reduction mechanism when using gears for the speed reduction mechanism built into the motor 6 cannot be ignored, determine the number of teeth of this speed reduction mechanism as appropriate and the period of speed unevenness of the toothed pulley itself. Against the pitch P of the above toothed belt 8 1 / (2n + 1) ... (However, n = 0, 1, 2, 3 ...) It should be designed so as to be.

【0026】

Although the printer has been described above as a printer in which the photosensitive head moves in the scanning direction to expose an image, it is also applied to a transmission system for moving the photosensitive paper in a printer in which the photosensitive head is stopped and the photosensitive paper is moved. It is also used in the scanner head movement mechanism of a scanner in which light receiving elements for reading images are arranged in a staggered manner like the photosensitive head, or in a transmission system for driving photographic paper in a form in which the head is fixed and the photographic paper is moved. Of course, it can be applied.

【0027】

[Effect of the invention]

As described above, the drive mechanism of the head using the toothed belt of the present invention in the transmission system has an advantage that it is possible to prevent color unevenness of the image caused by the synchronization unevenness of the traveling speed caused by the toothed belt. is there.

【0028】

In addition, by using a toothed pulley and a toothed belt instead of the pulley and wire rope used in the final stage of the transmission system for head movement, the poor workability caused by using the wire rope is eliminated. It is also possible to prevent a decrease in workability due to the miniaturization of the printer. In addition, the head module can be easily moved in the vertical direction, which has a practical effect of reducing the cost of the product.

[Simple explanation of drawings]

[Figure 1]

It is a perspective view of the printer which carries the drive mechanism of the head of this invention.

[Figure 2]

It is a perspective view which showed the outline of the transmission system of the printer of FIG.

[Fig. 3]

It is a schematic diagram which showed the structure of a photosensitive head.

[Fig. 4]

It is a figure explaining the occurrence of color unevenness by the moving speed unevenness of a photosensitive head.

[Fig. 5]

It is explanatory drawing which shows the example which prevented the occurrence of color unevenness.

[Fig. 6]

It is explanatory drawing which shows the condition which cancels the occurrence of color unevenness.

[Fig. 7]

It is a perspective view of a conventional printer.

[Fig. 8]

It is a perspective view which showed the outline of the transmission system of FIG.

[Fig. 9]

It is a schematic diagram explaining the cause of the speed unevenness of a toothed belt.

[Explanation of symbols]

1 chassis, 2 mounts, 3 guide shafts, 4 bearings, 6 motors, 7 toothed pulleys (drive side), 8 toothed belts, 9 toothed pulleys (driven side), 11 tension adjustment levers, 11b springs, 13 units Base, 13a fixing plate, 14 photosensitive head, 14a dot block,