FR2675738A1 - MATRIX PRINTING HEAD WITH SWING ARMATURE TYPE NEEDLES. - Google Patents

Abstract

The present invention relates to a matrix printing head with needles of the swing armature type, comprising a magnet yoke associated with each printing needle in a housing, an electromagnetic coil arranged on a branch of the magnet yoke, and an armature serving to drive the printing needles and closing the magnetic circuit. - According to the invention, a second additional magnetic circuit (10), mounted in parallel, is provided with the first magnetic circuit (9) extending over the magnet yoke and the armature (5), and the second circuit magnetic (10) extends over one branch (3a) of the magnet yoke, the armature (5), another magnetic resistor (11) and again into the armature (5) and through the other branch (3b) of the magnet yoke.

Description

The present invention relates to a print head

  needle matrix of the swing arm type,

  carrying a magnet yoke associated with each printing needle in a housing, an electromagnetic coil arranged on a branch of the magnet yoke, and an armature for driving the printing needles

and closing the magnetic circuit.

  Such dot matrix print heads are used for fast printing of large amounts of data in computer printers. The system of magnetic circuits determines the transferred energy that is

  necessary for printing with the help of

  pressing one or more recording media

arranged one above the other.

  In the rotating-arm type needle-matrix printing heads, the operating frequency is determined by the mass, the moment of inertia, that is to say also by the shape of the reinforcement. striving to keep the moving mass of the armature as small as possible The increase in the print frequency corresponds accordingly to the decrease in the mass of the armature. However, a decrease in the thickness of the armature is harmful to the vibratory behavior and to the expected mechanical resistance.

  to obtain the lowest possible thickness of the arma-

  A small thickness of the reinforcement has a negative influence

  the magnetic circuit in the armature between the two branches of the magnet yoke As the magnetic circuit of the armature possesses a maximum magnetic power between the two branches of the magnet yoke, the

  Armature cross-section acts there in a limiting way.

  This constriction limits the flux density in the radially outer portion of the frame and, thus, also the

  magnetic force created at this location.

  However, since the cross-sections of the armature and branches of the magnet yoke can not be kept identical because of the smallest possible thickness of the armature, there are still densities of

  different fluxes of the magnetic lines.

  Accordingly, the object of the invention is to generate a

  high magnetic force for the lowest possible mass of the armature and thus as low a thickness as possible.

  For this purpose, the dot matrix printing head of the type indicated above is remarkable according to the invention in that a second additional magnetic circuit, connected in parallel, is provided with the first one. magnetic circuit extending over the magnet yoke and the armature, and in that the second magnetic circuit extends on a branch of the magnet yoke, the armature, another magnetic resistor and again in the magnet. frame and

  through the other branch of the magnet yoke Thanks to this parallel resistance, the magnetic force

  tick is increased because the throttling is decreased. Advantageously, there is obtained at this location, at which the acceleration force is created, a higher flux density and, thus, a greater force. Another advantage is that the smallest cross-section possible or the the lowest possible thickness of the reinforcement can be used, so that an increase in mass in

movement is also avoided.

  Advantageously, at a distance from the armature, there is provided a magnetically conductive plate, which is arranged in the zone on the far side of the magnet yoke. The advantage is that this plate is fixed and must not be

  displaced like the armature This characteristic is deci-

  This is because, for fast systems (high operating frequencies), large magnetic forces for a small displaced mass are required. According to another characteristic of the invention, the zone, in which the magnetic resistance is arranged, encloses at least the space between the two branches of the magnet yoke. Thus, losses are advantageously avoided and, for a corresponding power, , we obtain a density of

  high flux of magnetic field lines.

  Preferably, the magnetic resistor is constituted by a continuous ring or individual segments, and is fixed in a part of the housing. Such a ring can, for example, be arranged, in a sufficiently precise manner, in a part of the housing.

  casing guiding the printing needles.

  In relation to the tolerances to be maintained, it is also advantageous that the distance between the magnetically conductive plate and the front face of the branches of the cylinder head

  magnet corresponds to an angular movement of the armature.

  The invention is not only limited to U-shaped magnet yokes, but can also be used

  for E-shaped magnet yokes, if the other resists

  magnetism or the magnetically conductive plate or the ring is opposed to the front faces of the branches of the

magnet yoke.

  The figures of the annexed drawing will make clear how

the invention can be realized.

  Figure 1 is a partial axial cross-section

  a dot matrix print head.

  Figure 2 shows a diagram of the field lines of a

  armature-magnet yoke system within a limited area.

  The hinged-type needle matrix printing head has a casing 1, in which there are arranged circumferentially distributed printing needles 2, to which is associated each time a magnetic yoke 3 with an electromagnetic coil 4 arranged on a branch 3a of the magnet yoke A frame 5 rests, by its radially inner portion 5a, against a damping disc 6 arranged in a fixed manner on the casing 1, and against a needle head 2a subject to

  force of a spring 8 and adjustable in the direction of im-

  pressure 7 The armature 5, a radially inner arm 3 b of the magnet yoke and the radially outer arm 3 a of the magnet yoke form a first magnetic circuit 9 A second magnetic circuit 10 extends radially on the arm external 3 a of the magnet yoke, the armature 5,

  another magnetic resistor 11 and again in the

  5 and through the other branch 3b of the magnet yoke The magnetic resistor 11 is formed by a plate 11a The plate 11a is in the area on the side 12 remote from the magnet yoke In FIG. , the

  magnetically conductive plate 11a is arranged in recou-

  the area of the branch 3a of the magnet yoke and the space between the two branches 3a and 3b of the magnet yoke. The magnetically conductive plate 11a consists of a ring 11b, which is fixed to a portion 1a of the housing. Inwardly, the ring 11b is fixed to the portion 1a of the housing by a peripheral centering flange 13 The distance 14 between the magnetically conductive plate 11a and the end face 15 of the legs 3a and 3b of the magnet yoke is determined in accordance with an angular movement or

the thickness of the frame 5.

  As can be seen in Figure 2, the other magnetic resistor

  11 or the magnetically conductive plate 11a or the ring 11b covers the front faces 15 of the branches 3a and 3b of the magnet yoke and, where appropriate, still

  other branches of the magnet yoke.

  As can be seen more easily in FIG. 2, part of the magnetic field lines of the magnetic circuit 10 passes through the plate 11a, so that also the

  power can be increased in the working gap.

  In branches 3a and 3b of the magnet yoke, the

  density of the field lines is obviously very high.

  A certain number of these lines of field is continued in the plate 11a. Within the zone determined by a calculation program (external framing), scattered field lines are also detected.

  however, there is a very low density of field lines.

Claims (5)

  A hoop-type needle dot matrix printing head having a magnet yoke associated with each printing needle in a housing, an electromagnetic coil arranged on a branch of the magnet yoke, and an armature for driving the printing pins and closing the magnetic circuit, characterized in that a second additional magnetic circuit (10), arranged in parallel, is provided with the first magnetic circuit (9) extending over the bolt magnet (3) and the armature (5), and in that the second magnetic circuit (10) extends on a branch (3 a) of the cylinder head   magnet, the armature (5), another magnetic resistor (11) and again in the armature (5) and through the other leg (3b) of the magnet yoke.   2 dot matrix printing head according to claim 1,   characterized in that, at a distance from the armature (5), there is provided a magnetically conductive plate (1a) which is arranged in the region on the side (12) remote from the magnet yoke (3).   The dot matrix printing head according to claim 1 or 2,   characterized in that the zone, in which the magnetic resistance (11) is arranged, encloses at least the space between the two limbs (3a, 3b) of the magnet yoke.   4 dot matrix printing head according to any one of claims 1 to 3,   characterized in that the magnetic resistor (11) is constituted by a continuous ring (11b) or individual segments, and is fixed in a portion (la) of the housing.   Matrix needle head according to one   any of claims 1 to 4,   characterized in that the distance (14) between the magnetically conductive plate (11a) and the end face (15) of the magnet yoke legs (3a, 3b) corresponds to a   angular movement of the frame (5).   6 Dot Matrix Printhead according to one   any of claims 1 to 5,   characterized in that the other magnetic resistance (11) or the magnetically conductive plate (11a) or the ring (11b) is opposite to the end faces (15) of the legs (3a, 3b) of the magnet yoke.