Serial recording apparatus

Abstract: In a serial recording apparatus wherein a recording head (7) is carried on a carriage (2) movable in the direction of print column and the recording head (7) is driven on the basis of printing data while scanning by the recording head, to thereby form a dot image on a sheet (5), piezoelectric elements (14A, 14B) are joined to a vibration plate (13) provided on the underside of the carriage (2) and the vibration plate (13) is slidably urged against the surface of a fixed member by a resilient force to thereby constitute a travelling wave type ultrasonic motor, and a travelling wave is generated in the vibration plate (13) by the piezoelectric elements (14A, 14B) being driven to thereby control the movement of the carriage (2).

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a serial recording apparatus for forming dot images on a sheet on the basis of print data while scanning in the direction of print column by a recording head carried on a carriage. Related Background Art As a recording apparatus for a printer, a facsimile apparatus or the like, use has widely been made of a recording apparatus of the type in which a recording head is carried on a carriage movable in the direction of print column and the recording head is driven on the basis of print data while scanning by the recording head, thereby forming dot images on a sheet, i.e., a serial recording apparatus. Figures 12 to 15 of the accompanying drawings are fragmentary perspective views showing the essential portions of the various types of the driving mechanism for said carriage. Figure 12 shows a carriage driving mechanism of the rack-and-pinion type. In Figure 12, a carriage 62 carrying a recording head 61 thereon is supported for movement along a guide shaft 63 and a guide rail 64. A pinion 65 rotated by a carriage motor (not shown) is supported on the carriage 62 and is in meshing engagement with an elongated rack 66 installed on the basis of a recording apparatus, and the position and movement of the carriage 62 can be controlled by controlling the rotation of the pinion 65 by the carriage motor. A rotary encoder 67 for detecting the rotation of the pinion 65 is mounted on the carriage 62. Figure 13 shows a carriage driving mechanism of the belt transmission type. In Figure 13, a carriage 72 carrying a recording head 71 thereon is connected to a belt 75 passed over a pair of pulleys 73 and 74. One pulley 73 is a driving pulley rotatively driven by a carriage motor 76, and the other pulley 74 is a follower pulley. Accordingly, the movement and position of the carriage 72 can be controlled by controlling the revolution of the motor 76. Figure 14 shows a carriage driving mechanism of the wire rope type. In Figure 14, a carriage 82 carrying a recording head 81 thereon is driven by a carriage motor 83 through a wire rope 84. The opposite ends of the wire rope 84 are connected to the carriage 82, and the wire rope 84 is passed over four guide pulleys 85A, 85B, 85C and 85D and the movement and position thereof are controlled by a driving pulley 86 rotated by the motor 83. Figure 15 shows a carriage driving mechanism of the lead screw type. In Figure 15, a carriage 92 carrying a recording head 91 thereon is threadably engaged with a threaded bar 93, which is rotatively driven by a carriage motor 94 through gears 95 and 96. The direction of movement and the speed of movement of the carriage 92 are controlled by the direction of rotation and the speed of rotation of the threaded bar 93. On the other hand, as a speed control system for keeping the speed of movement of the carriage constant, use has been made of an open loop system using a pulse motor, or a closed loop system in which the driving voltage of a DC motor or the oscillation frequency of a pulse motor is controlled in confirmity with the output of the encoder 67 as shown in Figure 12. Also, as regards the printing system in the recording head, the wire dot system, the heat transfer system or the piezo ink jet system is the mainstream, and the response frequency of each element (dot forming element) of the recording head is 1000 - 3000 Hz in the wire dot system, 500 - 1500 Hz in the heat transfer system, and 1000 - 3000 Hz in the piezo ink jet system, and further, the dot density in the image output by these systems is in the range of 7 dots/mm to 14 dots/mm. However, in the prior-art serial recording apparatus, the rotational movement of the motor for driving the carriage has been converted into rectilinear reciprocal movement through a rack and a pinion, pulleys and a belt, a wire rope or a lead screw as shown in Figures 12 - 15, respectively, and this has lead to the necessity of a mechanism portion for transmitting and converting the power, and to maintain dot position accuracy in the dot density area as previously mentioned, it has become necessary to increase the frequency of the pulse motor or to make the pitch of the encoder (such as the encoder 67 of Figure 12) fine and therefore, the carriage driving mechanism has been complicated in structure and it has been difficult to make it compact. There has also been the problem that due to the back-lash between the elements in the mechanism portion, the back-lash of the guide portion for rectilinear guide and further the back-lash of meshing portions such as gears, the noise of the carriage during the reciprocal driving thereof becomes so great that it is difficult to make the noise low. Also, the presence of back-lash in the mechanism portion has made it difficult to improve dot position accuracy. In the wire dot system, the heat transfer system and the piezo ink jet system which are the conventional printing systems, it is necessary from the limitations in the recording system to keep the printing period (the driving period of the recording head) constant and therefore, design is made such that the speed of movement of the carriage to be synchronized with the printing period is also kept always constant. The control for making the speed of the carriage constant has been executed by a method using a motor having a sufficient output torque in reserve in a case where the carriage driving motor is a pulse motor and open loop control is effected, and further has been executed also by a method of effecting speed control by a closed loop system of a DC motor or a pulse motor and an encoder. Here, description will be made of the relation between the printing operation and the speed of movement of the carriage in the various prior-art printing systems. Figures 16A to 16C of the accompanying drawings is a graph illustrating the timing of the printing operation of the wire dot system. Figure 16A shows the repeated printing period of the print wire, Figure 16B shows the time for which electric power is supplied to the magnet coil of each print wire of the wire dot head, and Figure 16C shows each flight cycle until the print wire begins to move and prints and returns. Figure 17 of the accompanying drawings is a schematic cross-sectional view of the wire dot head. In the case of the wire dot system, when the head response frequency is 2500 Hz approximate to the highest speed, the repeated printing period of the same print wire 52 is 400 µs {figure 16A} as shown in Figures 16 and 17, and usually the time for which electric power is supplied to the magnet coil 51 is set to the order of 200 µs {Figure 16B}. On the other hand, about 390 µs {Figure 16C}. is necessary as the shortest flight time from after the print wire 52 begins to move until it impacts the surface of a sheet (a recording medium such as printing paper) 53 and returns and therefore, under the condition approximate to the above-mentioned highest speed, the stable operation of the print wire 52 will be moved unless the fluctuation of the printing period is controlled to the order of 10 µs (400 µs - 390 µs). Also in the case of the piezo ink jet system, as in the case of the above-described wire dot system, the fluctuation of the speed of the carriage is limited by the time for the return of a piezo vibration plate and the return of the meniscus in the orifice, instead of the wire flight time. Further, in the case of the heat transfer system, it is very difficult to realize a printing period of frequency 2500 Hz and comparison at the same level is difficult, but a longer time for power supply is required as compared with the aforedescribed two systems and therefore, greater stability of the carriage speed becomes necessary. Figure 18 of the accompanying drawings diagrammatically illustrates the control system for the carriage driving system in the prior-art serial recording apparatus. In Figure 18, in the control circuit (MPU) 101 of the recording apparatus, there are provided an ROM 102 storing a control program, etc. therein and an RAM 103 including a working area such as a buffer register temporarily storing various data therein, and various data from a host apparatus are sent to the control circuit 101 through an interface (I/F). The control circuit 101 controls a recording head 105 through a head drive circuit 104 and also controls a carriage motor 108 through a motor timing control circuit 106 and a motor drive circuit 107, and further controls a sheet feed motor 110 through a sheet feed motor drive circuit 109. On the other hand, the output signal of an encoder for detecting the position and speed of the carriage is made by a photosensor 111, is shaped into a pulse wave form by a wave form shaping circuit 112, and is transmitted to the head drive circuit 104 and the motor timing control circuit 106, whereby the synchronizing control of the scanning of the carriage and the printing operation of the head is effected. As is apparent from the foregoing description, the carriage driving control system in the prior-art serial recording apparatus is of complicated construction. Figure 19 of the accompanying drawings is a fragmentary perspective view showing the construction of the carriage of a wire dot recording apparatus. In Figure 19, a recording sheet 121 as a recording medium such as printing paper or a plastic sheet is held in intimate contact with the surface of a platen 122 which serves also as a sheet feed roller, and a carriage 125 is movably supported by a guide shaft 123 and a guide rail 124 installed forwardly of and parallel to the platen. A wire dot head 126 containing therein a plurality of (e.g. 64) print wires and drive means therefor, and an ink ribbon cassette 127 for supplying an ink ribbon for transfer are mounted on the carriage 125. Figure 20 of the accompanying drawings is a fragmentary perspective view showing the construction of the carriage of a heat transfer recording apparatus. In Figure 20, forwardly of a platen 132 for backing up a recording sheet 131, guide shafts 133 and 134 are installed parallel thereto, and a carriage 135 is movably supported by these guide shafts 133 and 134. On the carriage 135, a thermal head 136 having a plurality of (e.g. 64) heat generating elements is supported for movement up and down, and an ink ribbon cassette 137 for supplying an ink ribbon for transfer between the thermal head 136 and the recording sheet 131 is further mounted. As is apparent from Figures 19 and 20, in the construction of the carriage of the recording apparatus of the wire dot system or the heat transfer system, the load with which the ribbon is taken up and the load with which the recording head 126, 136 contacts with the sheet 121, 131 and the ribbon are added as the load fluctuation elements during the movement of the carriage 125, 135, and this has also led to the problem that the carriage drive motor and the driving circuit therefor become bulky and complex. As described above, in the prior-art serial recording apparatus, even if various carriage driving methods and each printing method are combined skillfully, an attempt to execute highly minute printing at a high speed would lead to complex and bulky structure as well as to great energy of operation sound, and it has been very difficult or impossible to make the apparatus compact and light in weight and reduce the noise. In order to solve such problems, a second recording apparatus in which a recording head is carried on a carriage movable in the direction of print column and recording is effected on a sheet by the recording head and which uses an ultrasonic motor as a motor for driving the carriage is known from Japanese Patent Application Laid-Open No. 62-77968 and Japanese Patent Application Laid-Open No. 62-77969. In the driving of this conventional carriage using an ultrasonic motor, the construction has been simplified and the noise has been reduced, but no sufficient improvement has been made in making the apparatus compact and reducing the cost of the apparatus. In the drive system for the conventional carriage using an ultrasonic motor, the guide rail of the carriage is made into an endless annular shape and is used as the vibration plate of the ultrasonic motor and a surface wave is generated in this endless annular guide rail by two piezo motors of different phases and is used as a travelling wave to drive the carriage. The necessity of such endless annular guide rail leads to the formation of annular portions at the opposite ends of the guide rail, and such annular portions at the opposite ends have made the entire apparatus very bulky and costly. This has proved a great hindrance in instrumenting the carriage drive using an ultrasonic motor. Also, the US-A-4 672 256 describes an ultrasonic motor using the same kind of drive as the present invention. The ultrasonic motor disclosed therein comprises an elliptical vibration member on which a travelling vibration wave is generated by an electrostrictive element which is energized by a periodic voltage. A movable member is frictionally driven by the travelling wave on the straight portion of the vibration member. Therefore, a friction plate is secured to the underside of the movable member. However, also in this apparatus, the vibration member has a guiding function for the carriage. Since, therefore, only the straight portion of the vibration member can be used for driving the carriage, the size of the apparatus will become larger than in other driving systems. Additionally, the large size makes the recording apparatus more expensive. It is therefore an object of the present invention to provide an improved serial printer which will not become bulky even if an ultrasonic motor is used for driving the carriage. This object is achieved by serial recording apparatus in which a carriage carrying thereon a recording head is moved along a guide member in the direction of a print column, a movement of said carriage is detected by detecting means, and a control of timing of print by said recording head is effected by control means in response to a signal outputted from said detecting means, said serial recording apparatus being characterized in that said carriage is provided with an endless ringshaped vibration plate which has a contacting portion contacting said guide member and an electro-mechanical conversion element, said electro-mechanical conversion element is energized by high frequency pulses to generate a travelling wave, which is acted to said guide member at said contacting portion to move said carriage in the direction of said print column, and that said control means controls said timing of print of said recording head, generates high frequency drive pulses to said electro-mechanical conversion element and synchronizes said movement of said carriage and said control of timing of print of said recording head. Since, thereby, the vibration plate has no guiding function, the size of the vibration plate is independent of the range of movement of the recording head. Hence, the vibration plate does not have to cover the whole range of movement of the carriage. This enables a minimization of the ultrasonic motor. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of the essential portions of an embodiment of a serial recording apparatus according to the present invention. Figure 2 is a cross-sectional view of the essential portions of Figure 1. Figure 3 is a perspective view of the bottom surface of the carriage in Figure 1. Figure 4 is a block diagram of the control system of the recording apparatus of Figure 1. Figure 5 is a plan view of the vibration plate and the piezoelectric element in Figure 3. Figure 6 is a schematic fragmentary cross-sectional view of the essential portions of Figure 5. Figure 7A is a view showing the encoder of the recording apparatus of Figure 1 and Figures 7B to 7E are graphs showing the output wave form thereof and an ultrasonic motor driving pulse. Figures 8A to 8C are timing charts showing the driven state of the thermal ink jet head of Figure 1. Figures 9A to 9F are schematic longitudinal sectional views showing the ink discharge process of the thermal ink jet head of Figure 1. Figure 10 is a perspective view of the bottom surface of a carriage in another embodiment of the serial recording apparatus according to the present invention. Figure 11 is an exploded perspective view of the ultrasonic motor portion of Figure 10. Figure 12 is a perspective view showing a carriage driving mechanism of the conventional rack-and-pinion type. Figure 13 is a perspective view showing a carriage driving mechanism of the conventional belt transmission type. Figure 14 is a perspective view showing a carriage driving mechanism of the conventional wire rope transmission type. Figure 15 is a perspective view showing a carriage driving mechanism of the conventional lead screw type. Figures 16A to 16C are graphs showing the driving pulse wave form of a wire dot head. Figure 17 is a schematic cross-sectional view of the wire dot head Figure 18 is a block diagram of the control system of a prior-art serial recording apparatus. Figure 19 is a perspective view of the essential portions of a wire dot type recording apparatus. Figure 20 is a perspective view of the essential portions of a heat transfer type recording apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will hereinafter be described with reference to the drawings, and a first embodiment will first be described. Referring to Figures 1 and 2, the reference numeral 1 designates a base which is the standard of the structure of a recording apparatus, the reference numeral 2 denotes a carriage guided by guide portions 1a, 1b and 1c formed in the base 1 and sliding along the base 1, the reference numeral 3 designates a platen installed parallel to the direction of movement of the carriage 2, and the reference numeral 4 denotes a sheet feed roller for conveying a sheet (a recording medium such as recording paper) 5 inserted from an opening 1d in the base 1 through the front face (the printing portion) of the platen 3. An ink cartridge 6 constituting an ink tank is removably carried on the carriage 2, and in the example shown, a recording head (ink jet head) 7 formed with a plurality of ink discharge ports (orifices) 7a facing the platen 3 with a predetermined interval (e.g. 0.8 mm) is provided on the front portion of the ink tank 6. This ink jet head 7 can be formed integrally with the ink tank 6, or can be provided removably (for example, in the insertable fashion) relative to the ink tank 6. The base of an arm 8 pivotable about a pin portion 2a formed on the rear surface of the carriage 2 is pivotally mounted on the pin portion 2a, and a roller 9 is rotatably supported on a pin portion 8a formed at the tip end of the arm 8. This roller 9 is guided along the guide portion 1b (the downwardly facing surface). The arm 8 is biased by a coil spring 10 in a direction in which the roller 9 is urged against the guide portion 1b. The roller 9 is thus urged against the guide portion 1b, whereby the carriage 2 is urged from above against the guide surfaces of the guide portions 1a and 1c by the reaction force thereof, and the carriage 2 (more specifically, including a portion of an ultrasonic motor provided integrally with the carriage 2) is supported so as to slide along the base 1 in intimate contact therewith without any back-lash. A belt-like encoder 11 having light and shade or slits (windows) at a predetermined pitch is installed on the base 1. This encoder 11 is used to detect the position and speed of movement of the carriage 2 as will be described later. Referring to Figures 2 and 3, a vibration plate 13 is attached to the underside of the carriage 2 with a holding plate 12 interposed therebetween, and two pairs of piezoelectric elements 14A and 14B are stuck to predetermined locations on the vibration plate 13. The holding member 12 and the vibration plate 13 each are formed of an elliptical plate having a predetermined thickness and a size substantially equal to the width of the carriage, as shown in Figure 3, and are integrally stuck to the underside of the carriage 2 in a stacked state. Comb-teeth 15 concave and convex at a predetermined pitch in the direction of movement of the carriage are formed on that portion of the vibration plate 13 which is urged against and slides on the guide portion 1c of the base 1. The aforementioned two pairs of piezoelectric elements 14A and 14B are stuck to that area of the vibration plate 13 which is opposite to the comb-teeth 15, and are disposed with a predetermined interval (e.g. 1/4 of the full length λ of each piezoelectric element) provided between the two pairs of piezoelectric elements 14A and 14B. In Figures 2 and 3, a photosensor 16 for photoelectrically converting any variation in quantity of light based on the light and shade pattern or the windows (slits) of the encoder 11 is mounted on the underside of the carriage 2 at a location which embraces the encoder 11. A flexible printed plate 17 for power supply and for signal transmission is connected to the piezoelectric elements 14A, 14B and the photosensor 16. The reference numeral 18 in Figure 2 designates a pinch roller for urging the sheet 5 against the sheet feed roller 4 and providing accurate feed to the sheet 5. The plurality of ink discharge ports (orifices) 7a are vertically arranged in the front surface of the ink jet head 7 provided on the front of the ink tank (ink cartridge) 6, i.e., that surface of the ink jet head 7 which faces the platen 3. The vertically adjacent pitch of the ink discharge ports 7a is about 0.04 mm - 0.14 mm, i.e., of the order of 23.6 dots/mm - 7.1 dots/mm, and in the embodiments described hereinafter, unless specifically specified, it is to be understood that ink discharge ports of structure of 14.17 dots/mm are used. Figure 4 is a block diagram of the control system of the serial recording apparatus of Figures 1 and 2. In Figure 4, an ROM 27 storing a control program, etc. therein and an RAM 28 including a working area such as a buffer register temporarily storing various data therein are provided in the control circuit (MPU) 21 of the recording apparatus, and various data from a host apparatus are sent to the control circuit 21 through an interface (I/F). The control circuit 21 controls the ON and OFF of the heaters (printing elements) 7b of the recording head 7 through a head drive circuit 26 and also controls the supply of electric power to the piezoelectric elements 14A and 14B through a carriage drive circuit 24. Further, the control circuit 21 controls a sheet feed motor 23 through a sheet feed motor drive circuit 22. On the other hand, the position and speed of the carriage 2 are detected by the photosensor 16 (Figure 2) which cooperates with the encoder 11, and the detection signal thereof is shaped into a pulse wave form by a wave form shaping circuit 25 and is transmitted to the head drive circuit 26. Thus, the cynchronizing control of the scanning of the carriage 2 and the printing operation of the head 7 is effected. Description will hereinafter be made of the operation of the serial recording apparatus according to the present invention described with reference to Figures 1 - 4. When the control unit (MPU) 21 receives a detection signal indicative of the presence of a sheet (the supply of a sheet) after a recording sheet (a recording medium such as printing paper or a plastic sheet) 5 has been inserted through the opening 1d in the base 1, the sheet feed motor 23 is driven through the sheet feed motor drive circuit 22, whereby the sheet feed roller 4 is rotated and the sheet 5 urged by the pinch roller 18 is fed to the front of the ink discharge ports 7a. When a printing command is then given to the control system shown in Figure 4 from the outside through the I/F (interface), a desired high frequency current is sent to the piezoelectric elements 14A and 14B through the carriage motor drive circuit 24. Figure 5 is a plan view of the piezoelectric element of Figure 3, and Figure 6 is a fragmentary longitudinal sectional view showing the principle of the creation of the drive force by the piezoelectric elements. This piezoelectric element driving system constitutes a travelling wave type ultrasonic motor integral with the carriage 2. As shown in Figure 3, 5 and 6, this piezoelectric element driving system is comprised of the substantially elliptical vibration plate 13 stuck to the substantially elliptical holding member 12 and partly formed with the comb-teeth 15, the two pairs of piezoelectric elements 14A and 14B stuck to that side of the vibration plate 13 which is opposite to the comb-teeth 15, and the flexible printed plate 17 for supplying electric power to the piezoelectric elements 14A and 14B. As shown in Figures 5 and 6, the two pairs of piezoelectric elements 14A and 14B are stucked at an interval corresponding to 1/4 of the full length λ thereof (λ/4). The operation of the above-described piezoelectric element driving system (ultrasonic motor) will hereinafter be described. If the two pairs of piezoelectric elements 14A and 14B are called A phase and B phase, respectively, when alternating voltages expressed by the following equations EA = EO sinωt EB = EO sin (ωt + π/2) are applied to these A phase and B phase, the amplitudes of the standing waves created are: A phase standing wave: ZA = ZO sinK x sinωt B phase standing wave: ZB = ZO sin(KX + π/2) x sin(ωt ± π/2) and a travelling wave created by the combination of the A phase and the B phase is travelling wave: Z = ZA + ZB = ZO cos(ωt∓KX), where K = 2π/λ(wave number) , and ω = 2πf (angular speed) . Accordingly, by the travelling wave thus created, a thrust in the opposite direction to the travelling wave acts on the surface of contact between the comb-teeth 15 of the vibration plate 13 and the guide surface 1c of the base 1. The speed of movement V of the carriage 2 by this thrust is V = 4π · π · f · Z · e/λ, where Z = amplitude of the travelling wave, and e = 1/2 of the thickness of the vibration plate. As the values in the present embodiment, f = 40 KHz, Z = 1µ, e = 1.5 mm and λ = 10 mm and therefore, the speed of movement V of the carriage 2 is of the order of V = 236.6 mm/s ≒ 240 mm/s. Here, the value 40 KHz of the driving frequency f of the ultrasonic motor is a very high frequency as compared with the driving frequency 2 - 4 KHz of the conventional motor such as a stepping motor, and the use of the ultrasonic motor makes it possible to control the movement of the carriage 2 highly accurately. Figures 7A to 7E show the output wave forms made by the control system of Figure 4 on the basis of the signal from the encoder 11 when the carriage 2 is moved at a uniform speed, and the pulses supplied to the piezoelectric elements 14A and 14B. Figure 7A is a schematic view showing the arrangement of photosensors 16 each comprising a light-emitting portion 16A and a light-receiving portion 16B with the encoder 11 formed with openings (slits) at a predetermined pitch being interposed therebetween. When electric power is supplied to the piezoelectric elements 14A and 14B to drive the carriage 2 and the carriage 2 reaches a uniform speed range, an analog output as shown in Figure 7B is produced by the photosensors 16A, 16B of Figure 7A. This analog output is shaped into a pulse wave form as shown in Figure 7C by the wave form shaping circuit 25 of the control system of Figure 4, whereafter there is created a head driving pulse (dot pitch control pulse) of a predetermined period (in the shown example, 250 µs) as shown in Figure 7D. The horizontal axis of Figures 7A - 7E is a common axis representative of time or the carriage position. Figure 7E shows the ultrasonic motor driving pulse wave form of power supply period 25 µs applied to the piezoelectric elements 14A and 14B. Figures 8A to 8C are timing charts showing the driven state of the ink jet head 7. Figure 8A shows the driving signal of the ink jet head 7, i.e., the power supply pulse width and the power supply period, Figure 8B shows a heat current wave form flowing to the heater 7b of the thermal type ink jet head 7 which will be described later, and Figure 8C shows variations in the amount of protrusion and the amount of retraction of the meniscus (including the formation process of liquid droplet 7d) 7c in the ink discharge port of the thermal ink jet head 7 shown in Figure 9. The reference characters a, b, ..., f in Figure 8C indicate meniscus positions corresponding to the states of Figures 9A, 9B ... 9F. Figures 9A to 9F are longitudinal sectional views showing the ink droplet formation process near the ink discharge port (orifice) 7a of the thermal ink head 7. In Figures 9A to 9F, the reference character 7a designates the ink discharge port, the reference character 7b denotes a heater comprising a heat generating element, the reference character 7c designates the liquid surface tip end (meniscus) of ink near the ink discharge port, and the reference character 7d denotes an ink droplet. Figure 9A shows the standby state, Figure 9B shows a state in which bubbling has begun in the ink during the power supply to the heater 7b, Figure 9C shows a state in which the power supply to the heater 7b has been stopped and de-bubbling has begun and the ink droplet 7d is about to fly, Figure 9D shows a state in which the ink droplet 7d has departed and the liquid surface tip end (meniscus) 7c has retracted greatly, Figure 9E shows a state in which due to the reaction of the retraction of the meniscus in Figure 9D, the meniscus 7c has swollen from the ink discharge port surface, and Figure 9F shows a state in which the same standby state as Figure 9F has been restored. As illustrated in Figures 8A to 9F, according to the thermal ink jet system in which each ink discharge port is driven by the heater 7b, as compared with other recording systems, a very short power supply time (10 µs) and excellent responsiveness (the ink droplet discharging operation time is 180 µs) can be achieved. Therefore, even if the speed of movement of the carriage 2 fluctuates by the order of ±10% and the power supply period varies between 225 µs to 275 µs, the stability of ink discharge is maintained and thus, the carriage motor drive circuit 24 and the head drive circuit 26 are operable by completely discrete systems, and the drive circuit could be simplified. According to the embodiment described above, the ultrasonic motor using the piezoelectric elements 14A and 14B is used as the drive source of the carriage 2 and therefore, the mechanism for power transmission and conversion could be eliminated and a carriage driving system capable of being simplified in structure and being made compact could be realized. Also, the absence of the mechanism for transmitting and converting the power could result in the realization of a quiet recording apparatus in which the noise level during operation could be greatly reduced. At the same time, the responsiveness during operation could be enhanced (quickened). Further, by using the driving system of the piezoelectric elements 14A and 14B, the self-holding force works in the stopped state of the carriage 2 and therefore, any special mechanism for holding the carriage 2 is not required, and the absence of a winding portion leads to a very low level of the magnetic noise resulting from the flowing of electric current and therefore, any countermeasure for the magnetism emission noise as the apparatus (such as the printed plate structure or a magnetic shield sheath) is not required and accordingly, a serial recording apparatus which is simple in structure and can achieve a reduction in cost can be provided. Figure 10 is a perspective view of the carriage cartridge of a serial recording apparatus according to another embodiment of the present invention as it is inverted and seen from the underside thereof, and Figure 11 is an exploded perspective view of the carriage-mounted parts in Figure 10. In Figure 10, a piezoelectric element 33 and a vibration plate 34 are secured to the underside of a carriage 31 in a laminated state with a holding plate 32 interposed therebetween. Also, as in the case of Figure 3, a photosensor 16 and a flexible printed substrate 35 are mounted on the underside of the carriage 31, and the supply of electric power to the piezoelectric element 33 and the taking-out of the signal from the photosensor 16 are effected through the flexible printed substrate 35. In Figure 11, an electrode portion 35a electrically connected to the piezoelectric element 33 and the photosensor 16 and a connector 35b for connection to the control circuit 21 of the recording apparatus or to a circuit substrate taken out of the control circuit 21 are provided on the flexible printed substrate 35. The holding plate 32, the piezoelectric element 33 and the vibration plate 34 are all of a circular ring shape as shown in Figures 10 and 11, and comb-teeth 36 are formed on the surface of the vibration plate 34. A rotor (not shown) constituting an ultrasonic motor is rotatably supported on a shaft (not shown) concentric with the vibration plate 34 and provided on the underside of the carriage 31, and in the assembled state, one surface of the rotor is in contact with the vibration plate 34 and the other surface of the rotor is in contact with the guide surface 1c of the base 1 shown in Figure 1. To construct the ultrasonic motor, instead of using the rotor, the vibration plate 34 may be brought into direct contact (pressure contact) with the guide surface 1c of the base 1. The other portions of the embodiment of Figures 10 and 11 are substantially the same as those of the embodiment described with reference to Figures 1 - 8. According to the embodiment described above with reference to Figures 10 and 11, the same effect as that of the embodiment described with reference to Figures 1 - 9 has been obtained and in addition, since the shapes of the parts are similar circular shapes, the manufacture of the ultrasonic motor (the piezoelectric element driving system) and the carriage 31 has become easy and moreover, the effect that the thrust produced by the vibration plate 34 can be efficiently converted into a rectilinear force could be obtained by interposing the rotor. As described above, according to the serial recording apparatus of the present invention, an ultrasonic motor comprising the piezoelectric elements 14A, 14B, 33 and the vibration plate 13, 34 is used for carriage driving and therefore, it has become possible to construct a serial recording apparatus which can be simplified in structure and can be made compact and light in weight and in which the noise level during the operation can be greatly reduced and which has a self-holding force in the stopped state of the carriage and in which the magnetic noise during the driving of the piezoelectric elements is very small, and the stabilization of the quality of print, the high reliability and the reduction in the cost in the recording apparatus could be achieved. As is apparent from the foregoing description, according to the present invention, in a serial recording apparatus wherein a recording head is carried on a carriage movable in the direction of print column and recording is effected on a sheet by the recording head, a vibration plate driven by piezoelectric elements is provided on the underside of the carriage and use is made of a travelling wave type ultrasonic motor which enables the vibration plate to slide on a guide member on the base side and therefore, a construction which can made the apparatus compact to reduce the cost thereof and which can make the apparatus ready for production has been realized. Also, design is made such that the position and speed of movement of the carriage are detected and the printing period of the recording head is controlled on the basis of the detection signal and therefore, there can be provided a highly accurate serial recording apparatus in which even when the speed of the carriage changes, the position and printing timing of the carriage can be controlled highly accurately to thereby ensure a stable quality of print free of dot deviation.

Claims: A serial recording apparatus in which a carriage carrying thereon a recording head is moved along a guide member in the direction of a print column, a movement of said carriage is detected by detecting means, and a control of timing of print by said recording head is effected by control means in response to a signal outputted from said detecting means, being characterized in that said carriage (2) is provided with an endless ringshaped vibration plate (13) which has a contacting portion (15) contacting said guide member (1) and an electro-mechanical conversion element (14a, 14b) , said electro-mechanical conversion element (14a, 14b) is energized by high frequency pulses to generate a travelling wave, which is acted to said guide member (1) at said contacting portion (15) to move said carriage (2) in the direction of said print column; and that said control means (21) controls said timing of print of said recording head (7) , generates high frequency drive pulses to said electro-mechanical conversion element (14a, 14b) and synchronizes said movement of said carriage (2) and said control of timing of print of said recording head (7) . A serial recording apparatus according to Claim 1, characterized in that said vibration plate (13) is formed with a predetermined thickness and fixed to the underside of said carriage (2) with a holding plate (12) interposed therebetween. A serial recording apparatus according to Claim 1, characterized in that said contacting portion (15) of said vibration plate (13) is formed with comb-teeth (15) concave and convex at a predetermined pitch in the direction of said print column. A serial recording apparatus according to Claim 3, characterized in that said electromechanical conversion element is a piezoelectric device (14a, 14b) , said piezoelectric device (14a, 14b) is provided on the area opposite to said comb-teeth (15) of said vibration plate (13) . A serial recording apparatus according to Claim 4, characterized in that said piezoelectric device (14a, 14b) is a plurality of pairs of piezoelectric elements arranged at a predetermined interval.

Inventors: KIMURA TETSUO, SAITO TAKASHI, YOSHIMURA SHIGERU, KIMURA, TETSUO, SAITO, TAKASHI, YOSHIMURA, SHIGERU
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1989
Main classification: B41J19
IPC codes: B41J19