JPH04158050A - Print head - Google Patents

Abstract

PURPOSE:To suppress noise in printing by providing a back stopper which collides against an armature when an armature retracts and excited in a vibration mode in low sensitivity frequency band for human sense of auditory. CONSTITUTION:A back stopper 2 is made of a titanium alloy having high Young's modulus and resonance frequency for lateral vibration thereof is close to 19000Hz. Upon finish printing on a print paper, an armature 8 is returned by a spring 6 to a direction (b) and collides against an annular protrusion 2a of the back stopper 2 to be stopped at a regular stop position. At that time, the armature 8 collides against the back stopper 2 which thereby excited. But since the oscillation mode frequency of the back stopper 2 is 19000Hz, which is in very low sensitivity frequency band for general person, uncomfortable feeling is not caused in the user.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a print head used in a dot impact printer, and more particularly to a print head with low printing noise.

[Prior Art] An example of a conventional print head will be described. Each print wire is attached to the tip of an armature.

The other end of this armature is attached to a yoke. This yoke consists of an outer peripheral cylindrical part (hinge part) and a core pole arranged circumferentially on the inner side thereof, and a coil is wound around the core pole. When this coil is energized, the end of the armature to which the printing wire is attached is attracted, and the printing wire is pushed out. The tip of this printing wire presses against the printing paper through the ink ribbon, and printing is performed.

When the coil is de-energized, the armature is pushed back by the biasing force of the spring, collides with the huck stopper, and comes to rest. Conventionally, no consideration has been given to the vibration frequency of the vibration mode of the backstop in the direction of collision of the armature.

FIG. 6 is a frequency response analysis diagram obtained by calculating the frequency response of a general backstopper in a conventional print head using the finite element method, and there are resonance points near 6000H2 and 12000Hz. Therefore, noise having a resonance frequency at the resonance point is generated. The resonant frequency is included in a frequency band where human auditory sense is highly sensitive. Therefore, this collision causes the huck stopper to vibrate in an audible frequency band, and this vibration is the main cause of vibration noise or printer noise.

Therefore, as configurations capable of reducing such printer noise, conventionally known configurations include a configuration in which the collision speed of the print wire is reduced and a configuration in which the rigidity of each component constituting the print head is increased.

[Problem to be solved by the invention] However, as mentioned above, if the collision speed is reduced, the impact force will inevitably become smaller.

As a result, the force with which the ink ribbon is hit by the printing wire is weakened, and the ink is not sufficiently transferred to the printing paper, resulting in poor print quality.

In addition, by increasing the rigidity of each part that makes up the print head,
In general, the weight of the print head increases, which increases the weight of the product, and there are problems in that a large amount of torque is required to feed the line of the print head, and it becomes necessary to use a large motor for line feed.

The present invention has been made to solve the above-mentioned problems, and its purpose is to
Another object of the present invention is to reduce the printing noise of a dot impact printer without increasing the weight of the print head.

[Means for Solving the Problems] In order to achieve this object, the present invention drives an armature to which a printing wire is bonded and fixed at its tip, and as a result of this driving, the tip of the printing wire is placed on a printing medium. In the print head that performs printing by colliding with the armature, the backstopper collides with the armature when the armature retreats, and has a frequency of a vibration mode in a direction excited at the time of the collision in a frequency band where human hearing has low sensitivity. It is characterized by being prepared.

[Operation] According to the present invention having the above-described configuration, the armature returning to the retracted position after printing collides with the backst buckle and stops at a predetermined position. At this time, vibrational energy accompanying the collision is excited in the armature. However, the vibrations excited by the collision vibrate in a frequency band to which human hearing is insensitive or inaudible, and are radiated into the air at the same frequency. However, since this air vibration is insensitive to humans or outside the audible range, it does not cause pain to people nearby.

[Example] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

In FIG. 1, the area above the dashed line represents the outer shape of the print head, and the area below represents its cross-sectional structure.

A thin rectangular tube-shaped nose body 3 extends from the center of the front side (left side in FIG. 1) of the yoke 1, which constitutes the main part of the print head. This nose body 3 contains a plurality of (for example, 9
A printing wire 5 of the present invention is disposed, and the tip of the printing wire 5 is configured to protrude to the outside from a hole in a wire guide 4 provided at the tip of the north body 3. 20 Two other wire guides 4 are provided within the nose body 3 to guide the printing wire 5 to a proper position.

The base of the printing wire 5 is bonded and fixed to the movable tip of an armature 8 made of electromagnetic soft iron by means such as silver soldering. The armature 8 is biased by an armature return spring 6 to return it to its normal stop position.

A coil 7 attached to a core pole 1a formed on the yoke 1 constitutes an electromagnet in cooperation with the core pole 1a. When electricity is passed through this coil 7, the core pole 1 of the yoke 1
A magnetic attraction force is generated between a and the armature 8.

The outer rear end portion of the armature 8 is supported by the yoke 1 by a holding spring 9.

A back stopper 2 is attached to the rear of the armature 8 to position the armature 8 when it is not energized and to absorb shock. The material of this hack stopper 2 has a higher modulus of longitudinal elasticity than conventionally used resins, and has a relatively low mass of titanium alloy (6Ai-
6V-28n-Ti, 6Al-23n-4Zr-6Mo
-Ti, etc.) are used. As shown in FIG. 2, its shape is an annular ring with an inner diameter of 10.2 mm, an outer diameter of 33.4 mm, and a width of 5 mm.

This annular backstopper 2 has an annular convex portion on the left side in FIG.
It forms a U-shape. The width and height of the outer convex portion are each 1
．． 5 mm and 3.2 mm. The outer diameter, inner diameter, and height of the inner convex portion are 2.3 mm, 1. It is 0 mm.

FIG. 3 is a frequency response analysis diagram obtained by calculating the frequency response of the backstopper using the finite element method. The backstopper 2 used in this embodiment is made of a titanium alloy having a higher modulus of longitudinal elasticity than the material (resin) of the backstopper used in conventional print heads. Therefore, the resonance frequency of the backstopper 2 with respect to the lateral vibration in FIG. 1 is around 19,000 Hz.

The frequency range of pure tones that humans can perceive as sound varies considerably from person to person, or the frequency range that can be heard as sound is 20H
It is said to be about z to 20,000Hz. However, the human ear is most sensitive at frequencies around 2,000 Hz to 4,000 Hz, and becomes less sensitive as it moves to lower or higher frequencies. Therefore, the frequency range in which noise should be a problem is considered to be about 300 Hz to 16,000 Hz. Since the above-mentioned resonant frequency is outside this frequency band, the sensitivity of human hearing is low and there is no problem as noise.

In the above configuration, when the coil 7 is energized, a magnetic flux is generated in the coil 7, and this magnetic flux is transferred to the core pole 1.
It enters armature 8 through a.

The water then flows back from the armature 8 through the yoke 1 to the core pole 1a. At this time, a magnetic attraction force acts on the armature 8 toward the core pole 1a side, and the armature 8
move in the direction. As a result of this movement, the tip of the printing wire 5 strikes the printing paper via the ink ribbon, thereby printing on the printing paper. After printing on this printing paper, the armature 8 is returned to the direction b by the force of the armature return spring 6,
It collides with the annular convex portion 2a of the back stopper 2 and returns to the normal stopping position.

At this time, the armature 8 collides with the hack stopper 2, thereby causing the back stopper 2 to vibrate. However, as described above, the frequency of the vibration mode of this backstopper is 19,000 Hz, which is a frequency band to which ordinary humans are extremely insensitive, and therefore does not cause discomfort to the user.

In this way, the resonance frequency of the backstopper 2 is set to 300.
By setting the frequency above the frequency band of Hz to 16,000 Hz, the noise generated from the head can be reduced. FIG. 4 is a noise spectrum diagram comparing the noise of the conventional print head and the noise of the print head of this embodiment. The print head of this example had a sound reduction effect of 4.38 dB in acoustic power compared to the conventional print head.

It should be noted that the present invention is not limited to the embodiments described above, and various changes can be made without departing from the spirit thereof.

For example, in the above embodiment, the material of the back stopper used in the present invention is titanium alloy, which has a higher modulus of longitudinal elasticity than the material (resin) of the back stopper used in conventional print heads. However, the material is not limited to this material, and a resin material having a large modulus of longitudinal elasticity may be used. In addition to changing the material, the hack stopper may be reinforced with ribs as shown in FIG. 5 to increase the resonance frequency of the vibration mode perpendicular to the back stopper surface.

In addition, in the above-mentioned embodiments, a printing head is illustrated and described in which a driving force is generated in the armature by magnetic attraction force, and this driving force causes the printing wire to reciprocate to perform printing. The present invention is not limited to the above, and may be applied to a release type print head or a print head in which printing is performed by driving an armature using a mechanical driving force or a driving force generated when a voltage is applied to a laminated piezoelectric element. You can get the effect of

[Effects of the Invention] As is clear from the detailed description above, according to the present invention, the huck stopper of the print head has a resonance frequency of a vibration mode that vibrates in a direction perpendicular to the backstopper surface, which is low to human hearing. Since this is set in the sensitive area, the sound generated by the resonance of the backstopper does not pose a problem as noise. Therefore, the noise generated from the print head can be reduced without increasing the rigidity of the print head and increasing its weight, and without reducing the impact force and degrading print quality.

In addition, since the noise of the print head, which is the main cause of noise in impact printers, is fundamentally reduced, there is no need to install a soundproof cover around the print head or increase the degree of airtightness of the printer's body. Since the number of parts does not increase and the structure does not become complicated, it is possible to obtain an impact printer head with low manufacturing cost and low noise.

[Brief explanation of the drawing]

1 to 5 are detailed explanations of the present invention. FIG. 1 is a partially cutaway side view of the print head of the above embodiment, and FIG. 2 is a side view of the back stopper of the above embodiment. A perspective view showing the shape, FIG. 3 is a graph showing an analysis of the frequency response of the backstopper used in this example, and FIG. 4 is a noise comparison between the noise of a conventional print head and the noise of the print head of the present invention. The spectrum diagram and FIG. 5 are perspective views of a backstopper according to another embodiment of the present invention. FIG. 6 is a graph showing an analysis of the frequency response of a backstopper used in a conventional print head. , In the figure, 2 is a back stopper, 5 is a printing wire, and 8 is an armature.

Claims (1)

[Scope of Claims] 1. In a print head that drives an armature having a printing wire bonded and fixed to the tip thereof, and performs printing by causing the tip of the printing wire to collide with a printing medium as a result of this driving, the armature has the following steps: A print head characterized by comprising a back stopper that collides with the armature when retracting and has a frequency of a vibration mode in a direction excited at the time of the collision in a frequency band where human hearing has low sensitivity.