JPH05104745A - Printing head using piezoelectric element as actuator - Google Patents

Abstract

PURPOSE:To constantly keep a sinking amount of a printing wire at the time of impact substantially constant independently of the number of printing dots so far by a method wherein a voltage value of a piezoelectric element is varied in accordance with the stored value of the printing dot number so far. CONSTITUTION:Since a second leaf spring 33 securely bonded to a movable piece 35 moves relatively frontward with respect to a first leaf spring 31, a connecting part 37 rotates counterclockwise. In this manner, an arm 29 moves frontward in conjunction with the connecting part 37, and a printing wire 21 securely bonded on one end thereof is projected to abut on printing paper through an ink ribbon to print a dot on the printing paper. With the release of a voltage application, a piezoelectric element 25 is shrunk. This shrinking motion is transmitted to the arm 29 provided with the printing arm 21 to return the arm 29 to an inactive position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print head using a piezoelectric element as an actuator.

[0002]

2. Description of the Related Art Conventionally, in a piezoelectric element type print head,
By applying a constant voltage to the piezoelectric element, a charging / discharging current is flowed to expand / contract the piezoelectric element, and the expansion / contraction is expanded to drive the printing wire to perform printing. In order to improve the followability, this type of print head has a structure that does not greatly exceed the initial position when the print wire finishes printing and returns. As a specific configuration for this, the arm that serves to transmit the displacement of the piezoelectric element to the print wire is made to collide with a stopper fixed to a support frame that supports the piezoelectric element,
At the initial stage of printing, the gap between the arm and the stopper is set to almost zero and assembled.

[0003]

However, since the arm and the stopper are worn by colliding with each other, the gap between the two becomes large according to the number of print dots elapsed. When the position where the print wire finishes printing and returns greatly exceeds the initial position (hereinafter, this is referred to as the amount of subsidence), the followability of the print head becomes poor, and the impact force becomes too large to print. The wire may break the printing paper. The present invention has been made in order to solve the above-mentioned problems, and provides a print head capable of performing stable printing operation without changing the amount of subsidence depending on the number of elapsed print dots. With the goal.

[0004]

To achieve this object, the present invention provides a piezoelectric element with a charging / discharging current to expand / contract the piezoelectric element, and expand / contract the expansion / contraction to project or immerse the printing wire. In the print head for performing printing by means of the means, means for defining the potential of the piezoelectric element when the print wire is immersed,
It is provided with a storage means for storing the number of elapsed print dots or a value corresponding thereto, and a control means for controlling the potential of the piezoelectric element when the print wire is immersed according to the value stored in the storage means.

[0005]

In the above configuration, by changing the voltage value (initial potential with respect to the ground potential) of the piezoelectric element when the print wire is immersed, printing is performed regardless of the number of elapsed print dots in accordance with the stored value of the number of elapsed print dots. The amount of sinking when the wire is immersed can be kept almost constant at all times.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a control device of the present print head, FIG. 2 is a change diagram of applied voltage to a piezoelectric element of the print head, FIG. 3 is a sectional view showing a configuration of the present print head, and FIG.
FIG. 3 is a side view showing a configuration of a print unit 17 arranged on the print head. First, the configuration of the print head will be described with reference to FIGS. The print head is composed of a disk-shaped head body 13 and a bottomed cylindrical heat radiation cover 15, and has a cylindrical shape.
Material 5 is made of aluminum alloy. Printing unit 1
A predetermined number of 7 are radially arranged inside the heat dissipation cover 15 on the back side of the head body 13. A hollow nose portion 16 is provided at a substantially central position of the head body 13 so as to project at a position facing an ink ribbon and a print sheet (not shown).

The printing unit 17 includes a piezoelectric element 25 in which piezoelectric ceramics are laminated to each other, and a printing wire 21 for printing on a printing sheet via an ink ribbon (not shown) by moving forward and backward in association with expansion and contraction of the piezoelectric element 25. And a motion transmission mechanism 14 for expanding and transmitting the expansion and contraction movement of the piezoelectric element 25,
It is composed of a support frame 27 that supports the motion transmitting mechanism 14 and the piezoelectric element 25. The support frame 27 is integrally formed in a U-shape by the main strut portion 27a, the sub strut portion 27b and the connecting rear end portion 27c so as to surround both side surfaces and the rear end portion of the piezoelectric element 25 in the stacking direction (longitudinal direction). Has been formed. The piezoelectric element 25 is applied to the main strut 2 by applying a voltage.
Along the 7a and the sub-column portion 27b, a stretching motion is performed in the stacking direction. Further, the temperature compensator 26 is fixedly inserted between the rear end portion of the piezoelectric element and the connecting rear end portion 27c of the support frame 27 so that the piezoelectric element 25 corrects only the reduced size due to the temperature rise. Is becoming The print wire 21 is arranged in the nose portion 16 of the head main body 13, and the nose portion 1
It is guided by a predetermined number of guide plates 23 provided in 6 so as to be movable back and forth.

The motion transmission mechanism 14 has a print wire 2 at the tip.
1 has a plate-shaped arm 29 having a fixed shape, and first and second leaf springs 3 for expanding the displacement of the piezoelectric element 25.
1, 33 and a movable element 35 mounted on the front surface of the piezoelectric element 25 and transmitting the displacement of the piezoelectric element 25 to the second leaf spring 33.
It consists of and. First leaf spring 31 and second leaf spring 3
3 is the same material having elasticity and has the same shape. Further, the first leaf spring 31 and the second leaf spring 33 are installed in parallel with each other, and the tips thereof are continuously provided to form a U-shape, and the continuously provided portion 37 includes the printing wire 21 of the arm 29. Is fixed to the end opposite to the one end where is fixed. The base end of the first plate spring 31 is fixed to the side surface of the main support column 27a, and the base end of the second plate spring 33 is fixed to the side surface of the mover 35.

In the motion transmitting mechanism 14 having the above-described structure, when a voltage is applied to the piezoelectric element 25 and the piezoelectric element 25 expands in the stacking direction, the mover 35 interlocks and moves forward (to the left in FIG. 3). To do. The second plate spring 33 fixed to the mover 35 tries to move forward relative to the first plate spring 31, so that the continuous portion 37 rotates counterclockwise. As a result, the arm 29 is interlocked in the forward direction, and the print wire 21 fixed to one end of the arm 29 is projected,
The printing paper is hit through an ink ribbon (not shown), and dots are printed on the printing paper. When the voltage application is released, the piezoelectric element 25 contracts, and this contraction movement is transmitted to the arm 29 having the print wire 21,
The arm 29 returns to the non-acting position. The arm 29
An arm stopper 39a made of resin is provided at the non-acting position, and comes into contact with the stopper 39b of the sub strut 27b to stop.

Further, the main strut portion 27a and the sub strut portion 2
A 4-node link mechanism member 41 is provided so as to straddle 7b. The material of the four-bar linkage mechanism 41 is a plate material that is elastically deformable, and the wide side plate part 41a and the long narrow plate part 41b are connected to each other on the auxiliary column part 27b, and the shape thereof is a U-shape. Both ends of the plate portion 41b are main strut portions 27a
And the sub-column 27b. A notch hole 43 having a substantially H shape in a side view is formed in the plate portion 41a, and two sides sandwiching the notch hole 43 are fixed to the sub strut portion 27b and the mover 35, respectively. For this reason, when the piezoelectric element 25 expands and the mover 35 moves, the two sides of the plate portion 41a are elastically deformed into a parallelogram shape in a side view, and are configured not to hinder the mover 35 from moving. There is.

With the action of the moment in the counterclockwise direction of the connecting portion 37 of the motion transmitting mechanism 14, the piezoelectric element 2
5 may be bent in a direction intersecting the stacking direction,
Due to the configuration of the four-node link mechanism member 41, a moment in a direction of moving the mover 35 and the piezoelectric element 25 in the clockwise direction is generated, and thus these two opposite moments cancel each other out, and the piezoelectric element 25 is bent. It can be expanded and contracted linearly without doing. In addition, in each printing unit 17, the front end portion (the left end portion in FIG. 3) of the main support portion 27a is attached to an annular mounting piece 45 fixed to a predetermined position on the back surface of the head body 13 with a screw (not shown).
It is fixed to the head body 13 by being fixed with screws 19. Further, a lead wire 51 for connecting the piezoelectric element 25 to a drive circuit is provided at a predetermined position on the rear end portion of the support frame 27 in each printing unit 17, and the heat dissipation cover 15 is provided.
Is connected to the substrate 57 supported on the back side of the bottom surface of the.

Next, the control device for the print head will be described with reference to FIG. Print data is input from the personal computer 65 to the CPU 67 of the printer. The print dot number corresponding to the print data input to the CPU 67 is stored in the elapsed print dot number storage unit 61 in a form of being added to the print dot number up to now for each print wire. This storage means is composed of a non-volatile RAM, and retains the stored contents even when the power is off. The CPU 67 compares the number of print dots stored in the elapsed print dot number storage means 61 with a value stored in the ROM 71 in advance. Then, a command is output from the CPU 67 to the reference potential control means 63 so that the reference potential value of the drive voltage of the print head according to the number of elapsed print dots is reached. After that, the CPU 67 sends the print data to the print head drive circuit 69 (FIG. 5) to drive the print head 73.

Next, the relationship between the applied voltage to the piezoelectric element of the print head and the number of elapsed print dots will be described with reference to FIG. First, when the print unit 17 is assembled to the print head in manufacturing the print head, the piezoelectric element 25 is applied with a voltage when the arm 29 is fixed to the continuous portion 37. Arm stopper 39a at this time
And the stopper 39b are brought into contact with each other, and the pressure contact force thereof is made substantially zero. The voltage at this time is Vb. Printing unit 1
As shown in FIG. 2, when the number of elapsed print dots of the print wire is small (D1),
A potential obtained by adding the potential Vb to the ground potential is used as a reference potential. This potential is the voltage of the piezoelectric element when the print wire is immersed. When the fluctuation range of the voltage when operating the printing unit 17 is Va (constant value), the maximum potential applied to the piezoelectric element 25 is (Va + Vb). Then, as the number of elapsed print dots increases, the value of the shift amount E1 (initial value Vb) from the ground potential is sequentially decreased by the reference potential control unit 63 according to the value of the storage unit 61 that stores the number of elapsed print dots. I will do it. In FIG. 2, the number of elapsed print dots is D1 <D2 <D3 <D4, and the value of the shift amount E1 is sequentially reduced according to the number of elapsed print dots.

The total number of dots and the shift amount E1
According to an experiment by the applicant, the total number of dots and the wear amount of the arm stoppers 39a and 39b have a substantially proportional relationship. Further, the relationship between the applied voltage and the displacement amount of the piezoelectric element is almost proportional. Therefore, in this embodiment, the relationship between the total number of dots and the shift amount E1 is linearly decreased from Vb to 0 V at the guaranteed maximum number of dots, as shown by the alternate long and short dash line in FIG. It has a stepped shape that follows. The inclination of this straight line corresponds to the amount of wear during dot formation. That is, the amount of sinking of the print wire caused by the amount of wear can be canceled. In other words, the initial shift amount Vb is a value inevitably determined from the guaranteed maximum number of dots and the inclination.
By doing so, the arm stopper 39a and the stopper 39b in the non-driving state are kept in contact with each other with almost no pressure contact force up to the guaranteed maximum number of dots. It should be noted that the shift amount is always set to 0 volt when driving exceeds the guaranteed maximum number of dots.

By doing so, according to the progress printing,
The initial position of the connecting portion 37 on the tip side of the piezoelectric element is displaced, so that the arm 29 is stopped by the stopper 39b on the auxiliary column 27b.
Translate in the direction of. As a result, it is possible to prevent an increase in the gap between the arm side stopper 39a made of resin and the stopper 39b on the auxiliary column portion 27b due to wear. In other words, it is possible to prevent an increase in the amount of subduction.

FIG. 5 shows an example of a drive circuit of the piezoelectric element 25 for performing the above operation. In this embodiment, the DC variable power source 52 (voltage V1), the transistor Tr1 which is a switch element, the coil 53 and the piezoelectric element 25 are sequentially connected in series, and the negative electrode side of the power source 52 and the negative electrode of the piezoelectric element 25 are electrodes. The side is grounded. Transistor Tr
The forward direction of 1 is the forward direction from the positive electrode side of the power supply 52 toward the electrode side of the piezoelectric element 25 that should be the positive electrode. further,
The connection point between the transistor Tr1 and the coil 53 is grounded via the transistor Tr2. Transistor Tr2
Is the direction toward the ground point of the transistor Tr1 and the coil 53. Diodes D1 and D2 are connected in parallel to the transistors Tr1 and Tr2, respectively, and the forward direction of each diode D1 and D2 is opposite to the forward direction of each transistor. The positive electrode side of the power source 52 and the electrode side of the piezoelectric element 25, which should be the positive electrode side, are connected by a diode D3, and the forward direction of the diode D3 is opposite to the forward direction of the circuit.

Further, a diode D4 and a second DC variable power source 54 (voltage V2) are connected in parallel to the piezoelectric element 25, and the forward direction of the diode D4 is from the electrode side of the piezoelectric element 25, which should be the negative electrode, to the positive electrode. The direction is toward the electrode side which should be. Further, the transistor Tr1 is turned on and off by the CPU 67 via the transistor Tr3, and the transistor Tr2 is directly turned on by the CPU 67.
N, OFF control is performed. The variable DC power supplies 52 and 54 are power supplies controlled by the reference potential control means 63 of FIG.

With the above configuration, the CPU 67 turns on the transistor Tr1 by outputting the charging signal P1. Then, a current flows from the power source 52 to the piezoelectric element 25 through the transistor Tr1 and the coil 53, and therefore the coil 53 and the piezoelectric element 25 are charged while resonating, and the piezoelectric element 25 is displaced (extended). As a result, the printing operation is performed. After the set ON time has elapsed, the CPU 67 turns off the transistor Tr1 and waits for a certain period of time for sufficient printing. In this state, the electric energy of the coil 53 is regenerated by the power source 52 by the closed circuit including the coil 53, the diode D3, the power source 52, and the diode D2. In the OFF state of the transistor Tr1, the voltage of the piezoelectric element 25 decreases as its electric energy is consumed. After that, the CPU 67 causes the discharge signal P2
To turn on the transistor Tr2,
Wait for the set time. As a result, the electric charge charged in the piezoelectric element 25 is discharged, and the displacement of the piezoelectric element 25 is returned to the initial position. After that, the transistor Tr2 is turned off.
F This completes one stroke operation. Note that if the ON time of the transistor Tr2 due to the discharge signal P2 is lengthened, the second DC variable power supply 54 will be in a short-circuited state, so it must be within π√LC / 2 hours (√L
C is the square root LC).

FIG. 6 shows the piezoelectric element 2 by the circuit operation described above.
5 shows the waveform of the voltage applied to No. 5. Here, the voltage V2 of the second DC variable power supply 54 corresponds to the above Vb, and the difference between the voltage V1 of the DC variable power supply 52 and the voltage V2 of the second DC variable power supply 54 is the above voltage Va (constant value). Becomes The present invention is not limited to the configuration of the above-described embodiment, and various modifications can be made.

[0020]

As is apparent from the above description, according to the present invention, by controlling the potential of the piezoelectric element when the print wire is immersed, the print wire is controlled according to the number of elapsed print dots or the stored value corresponding to the number of print dots. It is possible to prevent a change in the amount of sinking of the ink, and to obtain a print head with stable characteristics that does not depend on the number of elapsed print dots.

[Brief description of drawings]

FIG. 1 is a block diagram of a print head controller according to an embodiment of the present invention.

FIG. 2 is a drive voltage waveform for a print head according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a print head according to an embodiment of the present invention.

FIG. 4 is a side view of the printing unit of the print head according to the embodiment of the present invention.

FIG. 5 is a diagram showing an example of a drive circuit for a piezoelectric element.

FIG. 6 is a diagram showing a voltage waveform applied to a piezoelectric element.

FIG. 7 is a diagram showing the relationship between the total number of dots and the applied voltage.

[Explanation of symbols]

 21 printing wire 25 piezoelectric element 61 elapsed printing dot number storage means 63 reference potential control means

Claims (1)

[Claims] 1. A print head, wherein a charging / discharging current is applied to a piezoelectric element to expand / contract the piezoelectric element, and the expansion / contraction of the piezoelectric element is expanded / transmitted to cause the print wire to project and retract, thereby performing printing. Means for defining the potential of the piezoelectric element, storage means for storing the number of elapsed print dots or a value corresponding thereto, and control for controlling the potential of the piezoelectric element when the print wire is immersed according to the value stored in this storage means A print head using a piezoelectric element as an actuator.