JPS61199969A - Head gap automatic regulating mechanism - Google Patents

Abstract

PURPOSE:To make correction of detection error of paper thickness on the basis of assembling errors very easier as well as secure exact and stable operations of a printing head by a method in which the printing head is once pushed by a platen and on the pushing position, the position of the platen is set up. CONSTITUTION:When the tip of a printing head 5 is pushed up by a platen 1, a spring 22 is contracted, and a carrier 4 is rotationally moved to the direction of arrow A. Thereby, a detection piece 30 attached to the carrier 4 is detected by a sensor 7. After detection signals are sent out from the sensor 7, the platen 1 is lowered, and from the time when the piece 30 is separated from the sensor 7, drive pulse is counted. When the count value reaches a given value, a pulse motor 17 is held up. By these operations, a print gap corresponding to the thickness of a paper 40 can be set up.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an automatic adjustment mechanism for the so-called head gap, which is the distance between a print head and a platen in a printer such as a typewriter or computer.

Printers that insert printing paper between the print head and platen and form characters or figures on the paper by the printing head's wire embossing action or ink droplet ejection action are capable of producing accurate and beautiful printing. In order to obtain a pattern, it is necessary to adjust the head gap according to the thickness of the printing paper, and an adjustment mechanism is provided for this purpose.

1. Conventional technology - A head gap adjustment mechanism commonly used in the past is as follows:
Although this structure adjusts the head gap by moving the print head side forward and backward, a structure has also been proposed in which the head gap is adjusted by moving the platen side back and forth. For example, JP-A-57-
No. 152976 discloses that after the printing paper is sandwiched between a roller fixed to a platen that is movable forward and backward facing the print head and a cover plate provided on the print head side, the platen is moved a predetermined amount from that position. A structure is disclosed in which the head gap is set according to the paper thickness by retracting the head, and is disclosed in Japanese Patent Application Laid-Open No. 57-152975 and Japanese Patent Application Laid-Open No. 57-163.
Japanese Patent No. 588 discloses a mechanism for automatically adjusting the gap by mechanically or electrically linking a paper thickness detection mechanism and a platen movement mechanism.

Furthermore, in the conventional structure described above, paper thickness is detected by separately providing a pair of members that sandwich the paper in addition to the print head and platen. For example, Japanese Patent Laid-Open No. 50-53123 proposes a structure in which the head gap is adjusted by pressing the print head and the print head against each other with a constant pressure and retracting the print head by a predetermined amount from the pressed position.

1. Problems with the prior art - However, in the case where the paper thickness detection mechanism is provided separately from the print head and the platen, the printing paper is held between these detection mechanisms, which has the disadvantage that, for example, when copying paper is used, the paper gets smeared. Furthermore, there is a problem in that the paper thickness detection mechanism applies a feed load to the paper, which hinders accurate paper feeding. In addition, in a device that detects paper thickness by pressing the print head and platen against each other with a constant pressure across the paper, for example, if a structure is adopted in which the platen moves forward and backward while facing the print head in a fixed position, the print head Detection errors may occur due to play between the carrier supporting the platen and its guide, making it difficult to accurately detect the paper thickness. If an unexpected frictional force is applied to the device, there is a risk that the device will malfunction, and stable and accurate operation is often hindered.

Object of the Invention The present invention was made with the aim of solving the problems of the conventional automatic head gap adjustment mechanism as described above. It is an object of the present invention to provide a head gap adjustment mechanism that guarantees accurate and stable operation and that can extremely easily correct paper thickness detection errors due to assembly errors and the like.

-Structure of the Invention- To explain using the reference numerals of the illustrated embodiments, the automatic head gap adjustment mechanism of the present invention is provided so that the print head 5 can be freely retracted and biased toward its advanced position, and the print head 5 can be biased toward its advanced position. A sensor 7 for detection is provided, and a platen 1 facing the print head is provided so as to be movable forward and backward by an appropriate drive device 17, and a printing paper 40 is placed between the print head 5 and the platen 1.
The head gap is set by advancing the platen toward the print head with the head inserted, and then retracting the platen by a predetermined amount using the detection signal of the sensor as the origin. That is, in a mechanism that moves the platen 1 forward and backward toward the print head 5 to adjust the head gap, the print head 5 is provided so that when the platen 1 moves forward, the print head 5 retreats accordingly. The position of the platen 1 is set based on the retracted position of the platen 1.

One Embodiment - The figures show one embodiment of the present invention, in which Fig. 1 is a perspective view, Fig. 2 is a sectional view showing details of the upper guide portion of the carrier, and Fig. 3 is a side view showing the operation. , FIG. 4 is a flow chart of the operation.

1 and 3, reference numeral 1 indicates a platen, and reference numeral 2 indicates a guide rod 1 mounted parallel to the platen 1. , 3 is an L-shaped guide rail mounted parallel to the guide rod 2, 4 is a carrier that runs back and forth along the guides 2 and 3, and 5 is fixed to the carrier 4 and is opposed to the platen 1. 6 is a cam that pushes the platen 1 toward the print head 5, and 7 is a sensor that detects the rotating position of the carrier 4.

As shown in FIG. 1, the platen 1 has an arm 1 attached to a shaft 11 of a paper feed roller 10, which is fixed to the frame of the apparatus, for example.
2, and is attached to the print head 5 so as to be movable toward and away from the print head 5. Rollers 13 serving as cam followers are pivotally attached to both ends of the platen 1, and the platen 1 is urged downward by its own weight or by an appropriate spring.
is supported by the roller 13 coming into contact with the cam 6. The cam 6 is fixed to a camshaft 14, which is mounted at a fixed position on a frame (not shown) and connected to a pulse motor 17 via gears 15, 16. Therefore, when the cam 6 is rotated by the pulse motor 17, the platen 1 is pushed and moved by the cam 6. cam 6
The contour curve is a curve in which the amount of elevation of the platen 1 and the rotation angle of the cam 6 are proportional.

The carrier 4 is slidably and rotatably supported by a guide rod 2 mounted at a fixed position on the frame, and a guide rail 3 is held between a roller 20 and a sliding body 21 at the upper part of the carrier 4. The guide structure is shown in FIG. 2, and includes a roller 20 pivoted on a carrier 4' and a sliding body 21 urged toward the roller 20 by a spring 22.
The guide rail 3 is held between the guide rails 3 to allow movement of the carrier 4 along the guide rod 2, and to restrict rotation of the carrier 4 around the guide rod 2. Reference numeral 23 in FIG. 2 is a sleeve that holds the sliding body 21 in a manner that it can freely extend and retract, and 24 is a spring retainer.

The print head 5 is attached to the tip of an arm 4a extending horizontally below the carrier 4 supported as described above. Therefore, if the carrier 4 is rotated around the guide rod 2, the print head 5 will be attached to the platen 1. Move toward and away from the target. The rotation of the carrier 4 around the guide rod 2 is regulated by the roller 20 and the sliding body 21 urged by the spring 22. In other words, the print head 5 is directed toward the platen 1 by the spring 22. The extension end position is regulated by the roller 20.

A detection piece 30 is fixed to the upper part of the carrier 4,
A sensor 7 having a pair of opposing light emitting device 31 and light receiving device 32 is disposed at a position slightly apart from the position of the tip of the detection piece 30 in a steady state. This sensor 7 is
It is preferable that the distance between the detection piece 30 and the detection piece 30 can be finely adjusted using an adjustment screw or the like.

Next, the operation of the illustrated embodiment will be explained based on FIGS. 3 and 4.

The paper 40 whose thickness has not been detected is fed between the print head 5 and the platen 1 with the platen 1 lowered to the lowest end. Then, at the predetermined cue position, the paper 4
When the platen 1 stops, the pulse motor 17 is driven to rotate the cam 6 in the direction in which the platen 1 is raised. Then, the platen 1 presses the paper 40 between itself and the print head 5, and further rises to push up the print head 5. That is, when the platen 1 pushes up the tip of the print head 5, a rotational moment shown by arrow A in FIG. 3 acts on the carrier 4, and the spring 2
2 is compressed, and the carrier 4 rotates in the direction of arrow A.

Due to this rotation, the detection piece 30 fixed to the carrier 4 moves toward the sensor 7, and when the print head 5 is pushed up to a certain position, the detection piece 30 is detected by the sensor 7. The amount of movement of the print head 5 at this time may be small, and the sensor 7 is preferably provided sufficiently close to the detection piece 30.

After the detection signal is emitted from the sensor 7, the pulse motor 1
7 for several more pulses, and then the pulse motor 17 is reversed to lower the platen 1. And detection piece 30
The drive pulses given to the pulse motor 17 are counted from the moment when the sensor leaves the sensor 7, that is, the moment the detection signal from the sensor 7 disappears, and when the count value reaches a preset value, the pulse motor Hold 17. The predetermined value to be set is based on the amount of movement from when the detection piece 30 leaves the sensor 7 until the print head 5 reaches its advancing end, and the play between the print head 5 and the paper 40 necessary for printing. This is the number of pulses corresponding to the sum.

The above operation sets the print gap according to the thickness of the paper 40, but the reason why the platen 1 is raised several more pulses after the sensor 7 detects the detection piece 30 during the above operation is because the print head This is to avoid malfunctions due to hysteresis caused by play in the support mechanism of platen 1.
The reason why the position where the detection piece 30 separates from the sensor 7 during descent is used as the origin of the set value count is that the detection accuracy of the sensor is more accurate, and the occurrence of errors due to the above-mentioned history phenomenon and reversal of the pulse motor 17. This is to prevent

Effects of the Invention - Since the automatic head gap adjustment mechanism of the present invention described above detects the paper thickness by sandwiching the paper between the print head and the platen, it is necessary to provide an independent paper thickness detection mechanism. In addition, since the print head is once pushed by the platen and the platen position is set based on the pushed position, the platen position can be set extremely accurately, and the platen and print head can be set very accurately. There is no risk of malfunctions or errors occurring due to play in the support mechanism of the sensor, variations in frictional force, etc., and accurate and stable operation is guaranteed.Furthermore, the structure is extremely simple and inexpensive, and the sensor A feature is that errors in individual devices can be easily corrected by changing the set values of the position and the amount of descent of the platen.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, in which Fig. 1 is a perspective view, Fig. 2 is a sectional view showing details of the upper guide portion of the carrier, Fig. 3 is a side view showing the operation, and Fig. 4 is a flow chart of the operation. In the figure, 1 is a platen, 2 is a guide rod, 3 is a guide rail, 4 is a carrier, 5 is a print head, 6 is a cam, 7 is a sensor, 17 is a pulse motor, 20 is a roller pivoted on the carrier, 21 2 is a sliding body, 22 is a spring, 30 is a detection piece, and 40 is printing paper.

Claims (1)

[Claims] 1. A platen is provided so as to be able to move forward and backward in opposition to a print head that is freely retractable and biased toward its advanced position. A sensor is provided to detect a predetermined retracted position of the print head, and a sensor is provided to detect a predetermined retracted position of the print head. An automatic head gap adjustment mechanism in a printer, characterized in that the platen is advanced toward the print head with printing paper inserted between the platen and the platen is retreated by a predetermined amount using the detection position of the sensor as the origin. .