Printer apparatus

Abstract

 A mechanism for feeding recording paper is simplified in a printer apparatus. The printer apparatus is provided with a platen 1 disposed along a direction of the width of recording paper 2 and a thermal head 3 which is pressed against the platen 1 with the recording paper 2 therebetween to carry out the operation for printing information every one line. A linear type ultrasonic motor 5 is used as means for feeding the recording paper 2. The ultrasonic motor 5 feeds the recording paper 2 while being synchronised with the printing operation along a paper feeding direction F from a paper inserting side toward a paper ejecting side of the platen. The ultrasonic motor 5 includes an ultrasonic wave applying portion 5a and a pressure applying portion 5b. The ultrasonic wave applying portion 5a is brought into contact with the recording paper 2 on the paper ejecting side to apply the ultrasonic vibration. The pressure applying portion 5b presses the recording paper 2 against the ultrasonic wave applying portion 5a and converts the ultrasonic vibration into frictional force to draw out the recording paper in the paper feeding direction F.

Description

[0001] The present invention relates to a printer apparatus. More particularly, the present invention relates to a printer apparatus capable of directly feeding recording paper by using an ultrasonic motor as a drive source.

[0002] A general structure of a prior art printer apparatus will be briefly described with reference to Fig. 4 of the accompanying drawing. As shown in Fig. 4A, the printer apparatus is provided with a platen 101 and a thermal head 102. The platen 101 is held in such a manner that it can rotate around shafts 101a which extends along a direction of a width of recording paper (not shown). More specifically, a stepping motor 104 is connected to the shaft 101a through a gear train 103. After a speed of rotary motion of the stepping motor 104 is reduced by the gear train 103, that motion is transmitted to the shaft 101a and the platen 101 is intermittently rotated in a direction indicated by an arrow for paper feeding. The thermal head 102 is in the rear of and opposed to the platen 101 with the recording paper therebetween. The thermal head 102 is so held as to be capable of swivelling around a shaft 105, and a printing portion of the thermal head 102 is pressed against the recording paper when performing the printing operation. In this state, power-feeding the printing portion allows characters for one line to be printed on the recording paper. When printing of characters for one line is finished, the platen 101 rotates in a direction indicated by an arrow to feed through the recording paper feeding.

[0003] Fig. 4B shows a typical cross section of the printer apparatus illustrated in Fig. 4A. As shown in the drawing, the thermal head 102 is in the rear of and opposed to the platen 101 with the recording paper 106 therebetween. When the thermal head 102 swivels around the shaft 105, which is parallel with the shaft 101a of the platen 101, in the counterclockwise direction, the printing portion positioned above the shaft 105 is pressed against the platen 101. A spring member 107 is provided between the thermal head 102 and a frame 108 of the printer apparatus in order to impart this pressing force. On the other hand, when the thermal head 102 swivels in the clockwise direction against an impetus of the spring member 107, the printing portion of the thermal head 102 moves away from the platen 101.

[0004] The prior art printer apparatus employs the stepping motor 104 as a drive source for feeding the recording paper. In other words the rotary motion of the stepping motor 104 is transmitted to the shaft 101a of the platen 101 while it is decelerated through the gear train 103, and the recording paper 106 is fed by rotating the platen 101 at low speed. In this manner, there can be recognised an advantage such as that use of the existing stepping motor 104 as a drive source enables the stable supply or the simple structure of a drive circuit. However, a mechanism for transmitting the rotary motion of the stepping motor 104 to the platen and simultaneously decelerating that rotary motion is required as long as the stepping motor 104 is used as a drive source, and provision of the gear train 103 is essential as shown in, for example, Fig. 4. Further, use of the existing stepping motor 104 limits reduction in size or thickness of the printer apparatus. As mentioned above, a reduction mechanism such as a gear train is required in order to decelerate the rotary motion of the stepping motor 104, resulting in the complicated structure and increased cost. In addition, the stepping motor or the gear train produces some noise during the operation, and hence they may not be suitable for certain applications.

[0005] There has been developed a printer apparatus adopting a system for directly driving the platen by using a rotary type ultrasonic motor in place of the stepping motor, and Fig. 5 shows a typical structure of such a printer apparatus. The printer apparatus is provided with a platen 202 disposed along the width direction of recording paper 201 and a thermal head 203 pressed against the platen 202 for printing information for each line. A rotary type ultrasonic motor 204 is fixed to an end of the platen 202 to configure paper feeding means. That is, the ultrasonic motor 204 feeds the recording paper 201, in synchronisation with the printing operation, along the paper feeding direction from the paper inserting side toward the paper ejecting side of the platen 202 by directly driving the platen 202 to rotate. In order to establish synchronism between the printing operation of the thermal head 203 and the operation for feeding the recording paper 201 by the platen 202, a disc having at least one slit 205 is attached to the rotary shaft of the platen 202. A photointerrupter 206 is combined with the disc 205. The disc having the slit 205 and the photo-interrupter 206 constitute an encoder, and constant detection of the rotating position of the platen 202 ensures synchronisation between the operation for feeding the recording paper 201 and the operation for printing information by the thermal head 203. In this structure, the rotary type ultrasonic motor 204 is used to directly drive the platen 202, and the reduction mechanism such as a gear train in the prior art is no longer necessary, thereby simplifying the structure.

[0006] However, a large load is applied to the rotary type ultrasonic motor 204 in the system for directly driving the platen 202. In other words, the ultrasonic motor 204 must drive the platen 202 to rotate with the thermal head 203 being pressed against the platen 202, which requires a high-output torque. This limits high output of the rotary type ultrasonic motor 204, preventing practical use of the motor. Further, the inner structure of the rotary type ultrasonic motor is relatively-complicated, which is disadvantageous in terms of cost.

[0007] It is therefore an object of the present invention to realise the structure for solving the above-mentioned technical drawbacks in the prior art. That is, a printer apparatus according to the present invention is provided with a platen, a print head and paper feeding means as a basic structure. The platen is provided along a direction of a width of recording paper. The print head is pressed against the platen with the recording paper therebetween for printing information on the recording paper. The paper feeding means feeds the recording paper, while being synchronised with the printing operation along the paper feeding direction from a paper inserting side toward a paper ejecting side of the platen. As a characteristic matter, the paper feeding means consists of a linear type ultrasonic motor. The ultrasonic motor comprises an ultrasonic wave applying portion which is brought into contact with the recording paper on the paper ejecting side to apply the ultrasonic wave and a pressure applying portion which presses the recording paper against the ultrasonic wave applying portion and converts the ultrasonic vibration into frictional force in order to draw out the recording paper in the paper feeding direction.

[0008] According to the present invention, the recording paper is sandwiched between the ultrasonic wave applying portion and the pressure applying portion and the ultrasonic vibration is converted into frictional force to directly draw out the recording paper in the paper feeding direction. That is, the linear type ultrasonic wave motor is used to directly feed the recording paper, and hence an output from the linear type ultrasonic motor can be very effectively utilised for feeding the recording paper. The linear type ultrasonic motor operates at low speed with a high torque, thereby enabling direct drive with respect to the recording paper. Further, the friction drive is principally adopted, and the ultrasonic wave applying portion has high self-sustaining ability because it immediately stops on the spot when the power supply is turned off. Therefore, since the recording paper can be firmly fixed, it can be cut off by hand.

[0009] Embodiments of the present invention will now be described with reference to the accompanying drawings, of which:

Fig. 1 is a cross-sectional view showing a basic structure of a printer apparatus according to the present invention;

Fig. 2A is a cross-sectional view showing a typical structure of an ultrasonic motor constituting a primary part of the printer apparatus according to the present invention;

Fig. 2B is a cross-sectional view showing a typical structure of a piezoelectric device of the ultrasonic motor constituting the primary part of the printer apparatus according to the present invention;

Fig. 2C is a circuit diagram showing an example of a drive circuit portion for the piezoelectric device of the ultrasonic motor constituting the primary part of the printer apparatus according to the present invention;

Fig. 3 is a cross-sectional view of a primary part showing an example in which a superimposed piezoelectric device of an ultrasonic motor also serves as an oscillator in the printer apparatus according to the present invention;

Fig. 4A is a typical perspective view showing a prior art printer apparatus using a stepping motor as a drive source;

Fig. 4B is a typical cross-sectional view showing the prior art printer apparatus using the stepping motor as a drive source; and

Fig. 5 is a typical perspective view showing an example of a prior art printer apparatus using a rotary type ultrasonic motor as a drive source.

[0010] A best mode for embodying the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a typical cross-sectional view showing a structure of a printer apparatus according to the present invention. As shown in the drawing, the printer apparatus is provided with a platen 1 disposed along a direction of the width of recording paper 2 (direction perpendicular to the drawing). The platen 1 may be capable of swivelling, although this feature does not affect performance of the present invention. A thermal head 3 is pressed against the platen 1 with the recording paper 2 therebetween and performs the operation for printing information on the recording paper 2. A spring 4 is used for pressing the thermal head 3 against the platen 1. Although this embodiment uses the thermal head 3 as a print head, the present invention is not restricted to this type, and it is needless to say that any other kind of print head can be similarly used. It is characteristic of the present invention to use an ultrasonic motor 5 as means for feeding the recording paper 2. In other words, the ultrasonic motor 5 feeds the recording paper 2, while being synchronised with the printing operation of the thermal head 3, along the paper feeding direction F from the paper inserting side toward the paper ejecting side of the platen 1. The ultrasonic motor 5 is of a linear type and basically provided with an ultrasonic wave applying portion 5a and a pressure applying portion 5b. The ultrasonic wave applying portion 5a is brought into contact with the recording paper 2 on the paper ejecting side of the platen 1 to apply the ultrasonic vibration. The pressure applying part 5b presses the recording paper 2 against the ultrasonic wave applying part 5a and converts the ultrasonic vibration into frictional force to allow the recording paper 2 to be drawn out in the paper feeding direction F. Although one ultrasonic motor is used in this example, a plurality of ultrasonic motors may be arranged in parallel with the paper width direction depending on the situation.

[0011] The ultrasonic wave applying portion 5a consists of an oscillator 6 and a piezoelectric device 7. A pair of projections 8 are formed on the oscillator 6. The pair of projections 8 are in contact with the recording paper on the surface opposed to the pressure applying means 5b. The piezoelectric device 7 is jointed to the lower surface of the oscillator 6. The piezoelectric device 7 is split into two for receiving high-frequency voltages having phases A and B which are shifted from each other 90 degrees. The high-frequency voltages are supplied from a high-frequency power supply 9. On the other hand, the pressure applying portion 5b is made up of a pressing plate 10 which is brought into contact with the surface of the recording paper 2 and a pressure spring 11. The pressure spring 11 presses the pressing plate 10 against the projections 8 of the oscillator 6. In this manner, arrangement is made so as to sandwich the recording paper 2 between the pressing plate 10 and the oscillator 6. The high-frequency voltages having phases A and B which are shifted from each other 90 degrees and are applied to the piezoelectric device 7 to cause the pair of projections 8 to perform elliptic motion. This elliptic motion applies a drive force to the recording paper 2 through frictional force and moves the recording paper 2 in the paper feeding direction F. Adjustment of voltages having phases A and B supplied from the high-frequency power supply 9 enables synchronisation between the printing operation by the thermal head 3 and the operation for feeding the recording paper 2.

[0012] Here, the projections are formed on the oscillator, but they do not have to be necessarily provided, and a friction material may be disposed on the flat top of the oscillator.

[0013] In this way, the present invention uses the linear type ultrasonic motor 5 to directly drive the recording paper 2. A mechanism for feeding the recording paper can be therefore extremely simplified. Further, an output from the motor can be directly used for feeding the recording paper, thereby improving efficiency. Furthermore, the ultrasonic motor 5 produces less noise as compared with the prior art stepping motor, it is suitable for the applications requiring silence. In addition, since the ultrasonic motor 5 does not generate a magnetic field like a stepping motor, it can be preferably used in an environment that the magnetic field adversely affects in particular. Moreover, the sustaining force of the ultrasonic motor 5 can be further increased when the power supply is turned off, thereby firmly fixing the recording paper 2.

[0014] The structure and operation of the linear type ultrasonic motor will now be described in detail with reference to Fig. 2A. On the upper surface of the oscillator 6 are formed a pair of projections 8 and on the lower surface of the same are connected piezoelectric devices 7 which are divided in two. Application of high-frequency voltages having phases A and B which are shifted 90 degrees from each other to a pair of piezoelectric devices 7 causes each projection 8 of the oscillator 6 to demonstrate elliptic motion as indicated by each arrow. This elliptic motion allows the recording paper 2 to obtain drive force through frictional force and to be propelled in the paper feeding direction F. The stepping motor is current-driven whereas the ultrasonic motor 5 is basically voltage-driven, and realisation of low-voltage drive is desired when the ultrasonic motor 5 is applied in the printer apparatus. Further, an oscillating circuit must be incorporated as a drive circuit instead of a simple constant current circuit in order to output high-frequency voltage, which leads to some complication of the structure. As a specification of this drive circuit, the power supply voltage is 12V and the rated current is approximately 0.2 - 0.3A, for example. The ultrasonic motor 5 is actually driven by using, for example, an alternating voltage of 100 kHz, and its crest value is approximately 40 - 60Vp-p. A pressure applied to the ultrasonic motor 5 is approximately 1 kg, for example. It is to be noted that use of a superimposed piezoelectric device 7 in which a plurality of electrodes 7a and piezoelectric ceramics 7b are alternately superimposed one on another, as shown in Fig. 2B, can gain a high-output torque. In addition, as shown in Fig. 2C, a self-excited drive system in which the piezoelectric device 7 is employed in the oscillating circuit as a part of the drive circuit may be adopted. Incidentally, a switch SW is used when a direction of the ultrasonic motor must be changed.

[0015] Fig. 3 shows another embodiment of a linear type ultrasonic motor serving as a drive source for supplying the recording paper according to the present invention. The linear type ultrasonic motor used in this embodiment is constituted by a superimposed piezoelectric device 50 having electrodes 51a, 51b, 51c, ... and piezoelectric devices 50a, 50b, 50c, ... alternately superimposed one on another and, as different from the linear type ultrasonic motor in structure, the superimposed piezoelectric device 50 itself characteristically functions as an oscillator.

[0016] By configuring the linear type ultrasonic motor in this manner, the greater thrust can be obtained and the piezoelectric device does not have to be connected to the oscillator, thus realising the further inexpensive apparatus. Moreover, external electrodes 52a, 52b, ... are formed on one end surface of the superimposed piezoelectric device 50 in the superimposing direction, and predetermined electric drive signals are input to the respective external electrodes for drive. A pair of friction members 53 and 54 are mounted on the other end surface of the superimposed piezoelectric device 50 in the superimposing direction, i.e., the end surface with which the recording paper is brought into contact.

[0017] As mentioned above, according to the present invention, the linear type ultrasonic motor is used to directly drive the recording paper. This can extremely simplify the structure of the printer apparatus. The ultrasonic motor produces less noise as compared with the prior art stepping motor, and hence it is preferable to applications requiring silence. Moreover, since the ultrasonic motor does not generate a magnetic field like a stepping motor, it is desirable for applications that the magnetic field adversely affect.

[0018] While this invention has been described with reference to an illustrative embodiment, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is, therefore, contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.

[0019] The aforegoing description has been given by way of example only and it will be appreciated by a person skilled in the art that modifications can be made without departing from the scope of the present invention.

Claims

1. A printer comprising:

printing means comprising a platen (1) and a print head (3), the printing means disposed along a paper feeding direction and adapted to print on the surface of recording paper (2) positioned between the platen (1) and the print head (3);

paper feeding means comprising an ultrasonic motor (5); characterised in that the ultrasonic motor (5) comprises an ultrasonic wave applying portion (5a) which is brought into contact with and applies ultrasonic vibration to the recording paper (2); and a pressure applying means (5b) which presses the recording paper (2) against the ultrasonic wave applying portion (5a) thereby converting the ultrasonic vibration into frictional force to urge the recording paper (2) along the paper feeding direction.

2. The printer of claim 1 wherein the ultrasonic motor (5) is of a linear type for transmitting linear motion.

3. The printer of any preceding claim wherein the ultrasonic motor comprises a piezoelectric device (7) and an oscillator (6).

4. The printer of claim 3 wherein the piezoelectric device (7) induces an elliptic motion in the oscillator (6).

5. The printer of claims 3 or 4 wherein the oscillator comprises projections (8) extending from the oscillator (6) towards the pressure applying means (5b), said projections being for contacting the recording paper (2).

6. The printer of any of claims 3 to 5 wherein the piezoelectric device (7) comprises a multi-layer comprising alternate layers of electrodes (7a) and piezoelectric ceramics (7b).

7. The printer of any preceding claim wherein the paper feeding means urges recording paper (2) along the paper feeding direction in synchronisation with the printing operation performed by the printing means.

8. The printer of any preceding claim wherein operation of a switch (SW) reverses the direction of movement of the ultrasonic motor (5).

9. The printer of any preceding claim wherein the paper feeding means is positioned on the paper ejecting side of the printing means.

10. A printer apparatus comprising: a platen (1) provided along a direction of the width of recording paper (2); a print head (3) which is pressed against the platen (1) with the recording paper (2) therebetween for printing information every one line; and paper feeding means (5) for feeding the recording paper (2) while being synchronised with the printing operation along the paper feeding direction from a paper inserting side toward a paper ejecting side of the platen (1),
   the printer apparatus characterised in that the paper feeding means is constituted by an ultrasonic motor (5) provided with an ultrasonic wave applying portion (5a) which is brought into contact with the recording paper (2) on the paper ejecting side to apply ultrasonic vibration and a pressure applying portion (5b) which presses the recording paper (2) against the ultrasonic wave applying portion (5a) and converts the ultrasonic vibration into frictional force to draw out the recording paper (2)in the paper feeding direction.

Drawing