Recording apparatus

Abstract: The present invention provides a recording apparatus which has reduced the speed variation and vibration of the motor. The recording apparatus uses a step motor (106) as a driving source for means for carrying a carriage (105) mounted with recording means or a recording medium (126), and has control means that, on accelerating the step motor (106), controls so that the step motor (106) is driven with a shorter period than the mechanical time constant of the carrying means when the rotary speed of the motor (106) is less than a specified value, and so that the motor (106) is driven with a longer period than the mechanical time constant when the rotary speed of the motor (106) is more than the specified value.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a recording apparatus according to the preamble of claim 1. In particular it relates to a recording apparatus using a stepping motor as a driving source for a carriage mounted with recording means or as a driving source for carrying a recording medium. Related Background Art In a conventional serial type printer, a hybrid type or PM type (permanent magnet type) stepping motor is used as a motor for driving a carriage to move a recording head mounted on a carriage during recording. In such a case, the carriage is secured to a carrying belt, and this belt is rotated by a pulley installed to the rotation shaft of the stepping motor. The carriage is so constructed as to scan in the recording direction for recording by the movement of the belt attendant upon the rotation of the motor. Such a stepping motor synchronizes with an external pulse, and switches the exciting current to the motor exciting phase to drive it for rotation. If the exciting current is switched faster than a specified value, the rotation of the stepping motor rotor is slightly delayed, and an error step called "step-out" occurs. Such a step-out throws the movement of the recording head into disorder, causing a position slippage or image disturbance on the recorded image. Especially when the carriage is accelerated, it should be noted that the step-out tends to occur because the load due to inertia is great in addition to unstable rotation of the stepping motor. A motor control device in which a closed loop controls a conventional stepping motor to solve such a problem has been disclosed in the U.S. Patent No. 4,963,808, and, further, such a stepping motor used for a printer was previously proposed in the U.S. Patent Application Serial No. 302,196, filed January 27, 1989. That is, in a recording apparatus using a stepping motor as a driving source and moving a recording head to scan for recording, a detecting means for detecting the angle of rotation of the stepping motor rotor is provided together with a control means for closed loop controlling the drive of the stepping motor in accordance with a detection result of the detecting means. It has been proposed to solve the problem by open loop controlling, and not by closed loop controlling the drive of the stepping motor in this way. However, the open loop control of the stepping motor has further had the following problems. Since a stepping signal is applied to each exciting phase to rotate the rotor in the stepping motor, when the stepping motor is rotated at low speed, the rotation of the rotor generates vibration, causing noise. For example, Fig. 18A shows the relationship between rotary speed and time when the stepping motor has been rotated with the speed curve taken in a straight line so that acceleration is constant. In this case, vibration occurs in the rotation of the stepping motor causing noise as shown by numeral 80 when the driving frequency is about 100 Hz, i.e the resonance frequency of the stepping motor. To prevent noise due to vibration during such an acceleration, it has also been considered to rapidly increase the rotation frequency of the stepping motor to a specified number of revolutions. However, when the stepping motor is rotated at a specified speed higher than the resonance frequency of the stepping motor from the beginning, the step-out occurs, and, therefore, this method cannot be used. Accordingly, a desired rotary speed should be reached by accelerating after starting the rotation at a sufficiently low speed at the beginning. For this reason, the stepping motor was conventionally driven for rotation so that the speed variation from the start to a constant speed is a property shown by an exponential curve in order to rotate the stepping motor without causing both step-out and noise. In the above conventional example, however, the stepping motor rotor rotates late for a driving pulse applied to the motor when the carriage is accelerated for driving as mentioned above. For this reason, during drive at a constant speed, in which recording operation is started after the acceleration, overspeed (overshoot) or speed variation, etc. occurs. This does not allow the carrying speed of the recording head to reach a specified constant speed even at a position where the recording operation is started, and the recording precision lowers. Fig. 18B shows a speed variation of the carriage (recording head) when the stepping motor was driven for rotation in accordance with a conventional exponential curve, and numerals 81 and 82 show portions in which the overshoot and speed variation occurred respectively. If a speed variation occurs because of such an overshoot, etc. when, for example, vertical ruled lines are recorded over the entire recording area in both recording directions (recording is performed when the carriage goes and returns), the recording position of vertical ruled lines at both ends of the recording area slips by the motion of the recording head, and, as a result, each of them may not be recorded as one line. This is because a vertical ruled line at the right end is recorded after the speed of the recording head has become fully a constant speed when the carriage moves in the right direction, for example, while a vertical ruled line at the left end is recorded immediately after acceleration. On the contrary, when the recording head moves in the left direction, a vertical ruled line at the left end is recorded at a constant speed, while a vertical ruled line at the right end is recorded immediately after acceleration. To prevent such a disordered record, one may take a distance from the time the acceleration is over until the recording starts sufficiently long, and start the recording operation after these overshoots, etc. have ended. However, there are problems in that the recording time will be long because of an extra operation until a constant speed is reached since the acceleration is finished, and in that the width of the recording apparatus will be long more than necessary to secure such a distance. SUMMARY OF THE INVENTION It is the object of the present invention to correct the above defects by reducing the speed variation and vibration of the stepping motor for the recording apparatus. This object is solved by the features indicated in claim 1. Advantageously developed embodiments of the invention are subject-matter of the dependent claims 2 to 10. These object, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block circuit diagram showing the outline configuration of a printer according to a first embodiment of the present invention. Fig. 2 is an appearance perspective view of the major part of the recording portion shown in Fig. 1. Fig. 3A is a partial cutaway perspective view of the carriage motor shown in Fig. 1. Fig. 3B is a sectional view of the motor shown in Fig. 3A. Fig. 4 is a view showing a driving signal of the carriage motor shown in Fig. 1. Fig. 5 is a diagram explaining the step-driven operation of the carriage motor shown in Fig. 1. Fig. 6A is a flow chart of the circuit shown in Fig. 1. Fig. 6B is a flow chart of the circuit shown in Fig. 1 during acceleration processing. Fig. 7 is a diagram showing a variation of rotary speed of the carriage motor shown in Fig. 1. Fig. 8 is a sectional view in which an encoder is added to the motor shown in Fig. 1. Fig. 9 is a configuration view showing the major part of the recording portion of a printer according to a second embodiment of the present invention. Fig. 10 is a configuration view showing a first modified example of the recording portion shown in Fig. 9. Fig. 11 is a plan view of the carriage guide mechanism shown in Fig. 10, partially broken away. Fig. 12 is a perspective view showing the principal portion of Fig. 11. Fig. 13 is a speed characteristic diagram during rise of the carriage shown in Fig. 10. Fig. 14 is a fragmentary perspective view of the carriage guide mechanism in a second modified example of Fig. 9. Fig. 15 is a plan view of the carriage guide mechanism shown in Fig. 14, partially broken away. Fig. 16 is a perspective view explaining the disassembly and configuration of a recording head using the ink jet method. Figs. 17A to 17G are views explaining the principle of the bubble jet recording. Fig. 18A is a diagram showing a variation in driving speed of a conventional carriage motor during acceleration. Fig. 18B is a diagram showing a variation in driving speed of a conventional carriage motor in an overshot state. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a block diagram showing the outline configuration of an ink jet printer according to an embodiment of the present invention. In Fig. 1, a controlling portion 101 processes data received from a host computer 117, and also controls the entire printer. A recording portion 102 constitutes a working portion of the printer. A host computer 117 transfers recording data and various recording control commands into the printer according to this embodiment. An input portion 118 receives recording data from the host computer 117 and provides interface control. In the configuration of the controlling portion 101, numeral 111 is a CPU such as a microcomputer, which executes various controls in accordance with a control program stored in a ROM 112. A RAM 113 is used as a work area for the CPU 111, and stores various data received from the host computer 117 and various data relating to the control of the CPU 111. This RAM 113 includes, for example, a line memory 115 for storing recording data for one line, a position counter 116 for storing the scanning position of the carriage, etc. Time data, etc. from the CPU 111 is inputted into a timer 114, and when a time corresponding to the time data is counted, the timer notifies a lapse of a specified time by causing an interrupt, etc., for example, to the CPU 111. The configuration of the recording portion 102 will be described. A recording head 104 in the ink jet system is driven by a driver 103 in accordance with recording data from the controlling portion 101. A carriage 105 mounted with a recording head 104 is driven for carrying by a carriage motor 106. This carriage motor is a step motor in this embodiment, and is driven by a driver circuit 107. A pulse signal 25 which instructs a timing for switching the exciting phase of the carriage motor 106 from the controlling portion 101, is inputted into the driver circuit 107 which synchronizes with the timing of this pulse signal 25 for outputting a four-phase exciting signal 26. Fig. 4 shows an example of this timing, and in Fig. 4, the carriage motor 106 is driven for rotation by two-phase excitation. A sheet feed motor 109 consists of a stepping motor, for example, and is driven for rotation by the driver circuit 108. A power source 110 supplies power to the entire apparatus. Fig. 2 is an appearance perspective view of the major part of the recording portion 102 shown in Fig. 1. In Fig. 2, numeral 104 is an ink jet type recording head, for example, and a carriage 105 mounted with a recording head 104 reciprocates in the arrow R and F directions along guide shafts 122 and 123. A timing belt 121 is connected to the carriage 105 at both ends thereof, and is stretched between pulleys 124 and 125. A carriage motor 106 drives the carriage 105 through the timing belt 121 for carrying. A recording sheet 126 is held by a platen (not shown), etc. at a position opposite to the recording head 104, and recording is successively performed by scanning of the carriage 105. The carriage 105 is provided with a masking shield 127. This masking shield 127 passes through a slit 129 in a photosensor 128 to cover the light, and it is thereby detected that the carriage 105 has arrived at the home position. This initializes the position counter 116 of the RAM 113 to "0". As the carriage moves in the F direction, that is, in the right direction from this initial position, its position is detected when the position counter 116 counts the pulse signal 25 for switching the excitation of the motor 106. At this time, recording is performed on a recording sheet 126 at the same time. After the carriage 105 performs a travel corresponding to recording for one line, the sheet feed motor 109 is driven for a specified amount of rotation to carry the recording sheet 126 only for one line in the arrow E direction. Figs. 3A and 3B are views showing an example of the configuration of the above-mentioned carriage motor 106. In Figs. 3A and 3B, numeral 130 is a rotor of the carriage motor 106, numeral 131 is a rotor shaft, numerals 132 and 133 are a stator located around the rotor 130, and numerals 134 and 135 are coils. The recording operation of the above-mentioned ink jet printer will be described referring to the flow charts in Figs. 6A and 6B. A control program corresponding to this control operation is assumed to have been stored in the ROM 112. This control processing is started when start of recording processing for one line is ready after recording data for at least one page or one line has been transferred from the host computer 117. Firstly, in step S1 it is judged from a signal from the photosensor 128 whether or not the carriage 105 is located at the home position at the left end in Fig. 2, and when not at the home position, the carriage motor 106 is driven in step S2 to move the carriage 105 to the home position. When the carriage 105 thus arrives at the home position, proceed to step S3 to initialize a position counter 116, etc. Then proceed to step S4, and follow the recording mode, etc. instructed by the host computer 117 to determine the speed and direction of rotation of the carriage motor 106. Determine a driving pulse number of the carriage motor 106 to be required for recording of one line from an amount of recording data to be recorded on one line. Proceed to step S5, and output a pulse signal 25 for instructing to rotate the motor, to the driver circuit 107 for accelerating. This acceleration will be described in detail referring to the flow chart in Fig. 6B. When the movement of the carriage 105 is thus started, the CPU 111 synchronizes with the pulse signal, counts up a position counter 116, and detects the position of the carriage 105 based on the discrete value. After acceleration is finished in step S6, judge whether or not the carriage 105 has arrived at the record-starting position, and if arrived, proceed to step S7 to start the recording operation by driving the recording head 104. Recording is actually started when the carrying speed of the carriage 105 has become constant. Then in step S8, view from the discrete value, etc. of the position counter 116, whether or not the carriage 105 has arrived at a record-finishing position for one line, that is, recording for one line was finished. If recording for one line has not been finished, return to step S9, and further output a pulse signal 25, and drive the carriage motor 105 at a constant speed. Although not specially mentioned in detail here, set a time corresponding to the exciting period of the motor 106 to the timer 114 for each time of excitation even while the carriage motor 106 is rotating at a constant speed, and the carriage motor 106 is driven for rotation at a constant speed whenever a timing signal (such as a time-out signal) from the timer 114 is input. After recording of one line is finished in step S8, proceed to step S10 to decelerate the carriage motor 106 by stopping the recording operation of the recording head 104. Then judge whether or not there is recording data for the next line. When there is no data for the next line but all recording processing is complete, proceed to step S13, and drive the carriage motor 106 to move the carriage 105 to the home position in order to complete the processing. When all recording processing is not yet complete, move the carriage 105 to the record-starting position of the next line to record the recording data for the next line, and return to step S4 again to execute the above processing. In the case of reciprocating record, the above-mentioned record-starting position of the next line is set to the right-end of the recording width of the next line. When moving the carriage 105 in the opposite direction (R-direction in Fig. 2) by reversing the carriage motor 106, the position of the carriage 105 is, of course, detected by deducting a value of the position counter 116 by the pulse signal 25 for calculation. The drive of the motor in the acceleration area will be described referring to the flow chart in Fig. 6B. When instructed to accelerate, proceed to step S21 to output a first pulse signal 25. This first pulse signal 25 generates an exciting magnetic field in the carriage motor 106 to hold the rotor 130 in a specified exciting position. This starts the rotation of the carriage motor 106 through a consecutive pulse signal row to be applied in step S22 and after that step. In step S22, start timing by the timer 114, and a pulse signal 25 is outputted in step S24 after a lapse of a specified time. Since then, the period of the pulse signal 25 to be outputted in steps S24 to S27 is assumed to be a time t₁ which is timed by the timer 114. This pulse interval t₁ is determined in the following way. That is, when the rotary speed of the carriage motor 106 is less than about a half of the rotary speed when recording is executed, the pulse interval will be less than a time interval (that is, a mechanical time constant of the carriage system) which the rotor 130 of the carriage motor 106 can follow up in step drive. Since this does not allow the rotor 130 of the carriage motor 106 to follow up a magnetic stability point which changes by switching the excitation, it rotates a little slower. For example, Fig. 5 is a diagram explaining the rotary position with respect to time when a step motor is step driven-by one exciting signal. A line shown by numeral 151 in Fig. 5 shows a profile of step operation of the step motor. As can be seen from Fig. 5, when it is step driven, the step motor rotates more than a specified amount of rotation after a lapse of a longer time than time B, and starts vibration thereafter. On the other hand, the motor rotates smoothly until time B is reached. Accordingly, when the motor is driven for rotation with a period shorter than time B, the motor rotary speed rises continuously and smoothly, and such a phenomenon will not be seen that the rotor 130 vibrates near the magnetic stability point as seen when the step motor is driven at a constant speed and accelerates together with speed variation. The carriage driving system shown in Fig. 2 consists of the carriage motor 106, the pulleys 124 and 125, the timing belt 121, and the carriage 105 mounted with the recording head 104. Also a sliding shaft 122 is related to the driving system through a frictional force. In this case, the mechanical time constant of the carriage system becomes a high value owing to the timing belt which is rich in flexibility, and the value ranges from about hundred scores to hundreds msec. Therefore, for the start of acceleration to a rotary speed of about a half of the final speed, an interval of switching the exciting phase of the carriage motor 106 may be shorter than this value. This is distinguished in step S27 in Fig. 6B. When the rotary speed of the carriage motor 106 is less than about a half of the constant rotary speed, return to step S24 to drive with a period of the above-mentioned time t₁. When the rotary speed increases and exceeds a half of the final speed, proceed from step S27 to step S28, and take an interval of the pulse signal 25 longer ( T = t₂ > t₁ ) than the above-mentioned time constant of the driving system. This is performed in steps S29 to S31. This enables the movement of the rotor 130 of the carriage motor 106 to follow up a speed of switching the excitation. Since, however, the vibration of the rotor 130 is suppressed by inertia force of the rotor 130 attendant upon the rotation at this point, speed variation such as vibration can be suppressed to a small value. Also at this point, the carriage motor 106 synchronizes with the pulse signal 25 for rotation, and therefore the rotor 130 rotates without speed variation even if the acceleration is finished and the carriage shifts to drive at a constant speed for recording operation in step S6 in Fig. 6A. That is, an overshoot due to reaction of the rotor 130, which occurs when the rotation of the rotor 130 is late for the pulse signal 25, will not occur. In Fig. 6B, when the rotary speed of the carriage motor 106 is less than a half of that during rotation at a constant speed (steps S24 to S26) and is more than a half of that during rotation at a constant speed (steps S29 to S31), it is shown that the pulse signal is outputted at regular intervals (t₁, t₂), respectively. However, it goes without saying that the period of the pulse signal 25 may be gradually shortened in steps S24 to S26 and steps S29 to S31. Fig. 7 is a diagram explaining the speed variation in the acceleration area of the carriage 105. It can be seen that, although a speed variation place is seen at a speed about a half of the final speed as shown by numeral 161 in Fig. 7, such an overshoot that occurs when the final speed is reached as shown in the conventional Fig. 18B, will disappear, and yet the speed variation converges within a short time. Near the speed variation place in the intermediate speed area in Fig. 7, the rotary speed of the carriage motor 106 is comparatively high, and, therefore, such noise as occurred with a conventional motor drive does not occur, but a quiet drive is possible. Accordingly, even if the carriage is driven at a constant speed for recording, the speed stability is improved, and no uneven record occurs. A time table which determines the output timing for the pulse signal 25 to drive the above-mentioned carriage motor 106, has been stored in the above-mentioned ROM 112, and is successively read out from the ROM 112 and set into the timer 114 from the CPU 111 when driving the carriage motor 106 for rotation. The exciting period for the carriage motor 106 is thus determined. Concerning the configuration of the carriage 105 and the carriage motor 106, the timing belt 121 is not directly rotated around the pulley 124 of the carriage motor 106 as shown in Fig. 2, but may be combined through one stage or several stages of timing gears. In the above first embodiment, the position counter 116 counts the pulse signal 25. In place of this, however, the following may, of course, be adopted: a detecting disk 137 which rotates together with rotation of a rotor shaft 131, is provided as shown in Fig. 8, the rotation of this detecting disk is detected by a photointerrupter 136, and a signal from this photointerrupter is counted by the position counter 116. According to the first embodiment of the present invention as mentioned above, the carriage motor 106 has no vibration in the acceleration operation, but yet quiet and quick acceleration operation can be performed, enabling the carrying of the carriage with good precision. Therefore, the carriage can be carried without vibration and uneven speed. The second embodiment according to the present invention will be described referring to Fig. 9. Fig. 9 is a schematic outside view showing the major part of the recording portion of a printer. In Fig. 9, a pulley 202 is coaxially installed to a carriage motor 201, and this pulley 202 is connected with a carriage shaft pulley 204 through a timing belt 203. This timing belt 203 is given a tension by a spring (not shown). A recording head 209 is mounted on a carriage 206. This recording head 209 has an ink tank within, whereby recording can be performed without receiving ink from other means. This carriage 206 is supported by a lead screw 252 and a sliding shaft 251 which are guide members, and records on a recording medium (recording sheet) by shifting on the above-mentioned two shafts. A recovery device 210 for the recording head is disposed at the home position (on the left side in Fig. 9) of this printer, and when the carriage 206 shifts and the recording head 209 arrives at the home position, recovery of the recording head 209 is performed. That is, when the carriage 206 arrives at the home position, a pressure contact spring 211a allows a gear 211, which has been pressed in the right direction in Fig. 9, to engage a recovery system gear 212 by pressing the gear 211 in the left direction in Fig. 9. Since a lead pin as mentioned later is in a groove 252b at this time, the carriage 206 does not shift right-to-left by the rotation of the lead screw 252. This engagement between the gear 211 and the recovery system gear 212 transmits the driving force of the carriage motor 201 to the recording head recovery device 210 to perform various operations such as cleaning the discharge surface of the recording head 209, and correcting clogging due to suction of ink. A sheet feed motor 213 drives a sheet feed roller 216 through a motor gear 214 and a roller gear 215 to carry a recording medium. Recording is performed on the above-mentioned recording medium by means of carrying of this recording medium, scanning of the carriage 206, and the recording head 209. In this example, single reduction is used for reduction of the sheet feed motor 213, however, the reduction is not limited to single reduction, but direct drive, in which the sheet feed motor 213 is direct-coupled with the sheet feed roller 214, or multiple reductions such as dual reduction may be used. The carriage 206 is driven for carrying by transmitting the driving force of the above-mentioned carriage motor 201 to the lead screw 252. As shown in Fig. 9, a spiral groove 252a is provided on the lead screw 252, and a lead pin 207 engages this groove 252a. This lead pin 207 is guided in the axial direction by a bearing portion provided in the carriage 206. A lead pin spring 208 is pressed against an end (on the other side of the lead screw 252) of the lead pin 207, and the lead pin 207 is pressed against a groove 252a in the lead screw 252. The other end of the lead pin spring 208 is mounted to the carriage 206. In the rear portion (a print head discharge portion 209a side is regarded as the front portion) of the carriage 206, the sliding portion 251 is disposed, and is supported by a pin of the carriage 206 and the carriage 206. When the lead screw 252 is driven for rotation by the carriage driving motor 201, the lead pin 207 mounted to the carriage 206 is guided by the groove 252a, whereby the carriage 206 and the recording head 209 record while reciprocating in the axial direction of the lead screw 252. In this embodiment, the carriage system consists of the carriage driving motor 201, the pulley 202, the timing belt 203, the carriage shaft pulley 204, the lead screw 252, the carriage 206, and the recording head 209. In this case, since the inertia of the lead screw 252 is great, the resistance during acceleration is great. Accordingly, the mechanical time constant of the carriage system is also high, being nearly hundreds msec. Also in this second embodiment, it is possible to carry without causing vibration and overshoot to the recording head 209 by giving such a driving pulse timing as mentioned above in accordance with the speed when accelerating the carriage motor 201 in the same manner as in the above-mentioned first embodiment. In Fig. 9 showing the second embodiment, it goes without saying that the carriage motor 201 may be connected with the lead screw 252 through a gear instead of the timing belt 203. A modified example of the above-mentioned second embodiment will be described referring to Figs. 10 to 13. The same portions as in Fig. 9 are affixed with the same numerals, and their concrete description will be omitted. In Figs. 10 to 12, a carriage push spring 217 is disposed between the lead screw 252 and the carriage 206 to energize the carriage in a direction which keeps the carriage away from the lead screw 252. This carriage push spring 217 is obtained by forming a long and narrow leaf spring into a specified shape, and is disposed along the lead screw 252. It is mounted to the carriage at the center, and is pressed against the lead screw 252 at the both ends thereof. According to such a carriage guide mechanism, since the carriage push spring 217 presses the lead screw 252 in the arrow P direction in Fig. 11, the movement of the carriage 206 in the guide direction (axial direction of the lead screw 252) is controlled. This enables smoothly shifting the carriage 206 at the rise time (lamp up from stop to target speed A) and at the fall time (lamp down from target speed A to stop) on driving the carriage 206. That is, we could realize smooth carriage driving by eliminating a unstable portion of the carriage moving speed brought about by inertia of the carriage and eliminating occurrence of the vibration noise when accelerating and decelerating. Fig. 13 is a speed diagram showing a fluctuation in the travel speed at the rise time of the carriage 206 shown in Fig. 10. When accelerating the carriage 206 to the target speed A in Fig. 13, we could stabilize at the target speed A immediately except one overshoot as shown in D portion in Fig. 13. We could considerably reduce a time E from zero speed to the target speed A as compared with a conventional time. By the foregoing, it is possible not only to reduce vibration noise at the rise and fall time of the carriage 206, but also to accelerate stabilization (stabilization to target speed) of travel speed and to shorten the travel distance of the carriage 206 at the lamp up and down time. Therefore, it has become possible to miniaturize and reduce the weight of the recording apparatus. Although the lead screw 252 was used as a guide member for the carriage 206 in the above examples, the present invention can be likewise enforced in a recording apparatus of a system, which uses a round shaft with a circular cross section and drives the carriage through a timing belt, etc., to have the same effect. Although the lead screw 252 was pressed at two places by the carriage push spring 217 in the above example, this pressing point may be changed to one place or more than two places. The above-mentioned carriage push spring 217 is generally made of metallic material, and in the case of metallic material, metal rubs against metal to possibly cause unusual noise when the carriage 206 moves. When such an unusual noise is likely to occur, it is desirable to coat solid lubricant on the surface (at least an area in contact with the lead screw 252) of the carriage push spring 217 to prevent direct contact between metals. For the solid lubricant, lubricating material such as molybdenum system of fluoroplastic system can be used. By thus coating solid lubricant on the carriage push spring 217, we could deaden frictional sound between metals when the carriage moves, and deaden or reduce vibrational noise due to unstable speed during the lamp up and down. Fig. 14 is a partial perspective view of a carriage guide mechanism according to a modified example of the second embodiment of Fig. 9, and Fig. 15 is a partial cutaway plan view of the carriage guide mechanism in Fig. 14. In Figs. 14 and 15, in place of the carriage push spring 217 of Fig. 11, a carriage push portion (spring portion) 218 corresponding thereto is formed as a portion of the carriage 206. A hatched portion 206c in Fig. 14 is a bearing portion formed in the carriage 206, that is, a portion fitting the lead screw 252. The carriage 206 is made of synthetic resin material, and, therefore, the carriage push portion 218 incorporated with the carriage is also made of the same resin material. The carriage push portion 218 has a U-shaped cross section as shown in Fig. 14, and is pressed against the lead screw 252 by the elastic force (spring force) of the U-shaped portion. The elastic force controls the movement of the carriage 206 in the axial direction of the lead screw 252. In this example, the elastic member (carriage push portion as a spring) 218, which is disposed between the carriage 206 and the guide member (lead screw) 252, is made of resin material, and, therefore, no frictional sound between the lead screw 252 and the elastic member occurs even if it is used as it is without performing noise generation preventive treatment such as the above-mentioned coating with a solid lubricant. Also, since the carriage push portion 218 as an elastic member is incorporated with the carriage 206, the cost can be reduced owing to a less number of components and less assembly man-hour than the above-mentioned modified example of the first embodiment. Although the lead screw 252 was used as a guide member for the carriage 206 in the above examples, the present invention can be likewise enforced in a recording apparatus which uses a straight guide shaft, etc. without any helical channel 252a, etc., to have the same effect. In a recording apparatus for recording by allowing a carriage mounted with a recording head to travel along a guide member in these examples, since it has been constructed so that an elastic member is provided between the carriage and the guide member, it is possible to reduce vibrational noise due to unstable speed at the lamp up and down time of the carriage, and to further shorten the static stabilization time to the target speed at the rise time, and the recording apparatus can be miniaturized and its weight can be reduced. In the present invention, the serial type bubble jet recording system, one of the above-mentioned ink jet recording systems, is used as recording means, and this system will be described below. Fig. 16 is a disassembly and configuration explanatory drawing of the recording head 209 which constitutes the recording means, and Figs. 17A to 17G are explanatory drawings showing the bubble jet recording principle. Its typical configuration and principle are disclosed in the U.S. Patents No. 4,723,129 and No. 4,740,796, for example. In Fig. 16, numeral 209a is a heater board, and an electric heat converter (discharge heater) 209b and an electrode 209c of aluminum, etc. for supplying electric power thereto are formed into a film and disposed on a silicon substrate. The recording head is constructed by bonding a top 209e having partitions, which partition a liquid path (nozzle) 209d for recording, to the heater board 209a. Also, in the specified place of the apparatus, an ink cartridge for feeding ink to the recording head 209 is mounted to the recording head 209 so that it can be replaced. Ink fed from the ink cartridge through a conduit is poured into a common liquid chamber 209g within the recording head 209 through a feed port 209f provided in the top 209e, and is led into each nozzle 209d from this common liquid chamber 209g. At these nozzles 209d, ink discharge ports 209h are formed, and the ink discharge ports 209h are formed at a specified pitch in the sheet carrying direction of the recording head 209 opposed to the recording sheet. This recording head 209 is mounted on a carriage capable of reciprocating, and synchronizes with the travel of the carriage to record by discharging ink. The principle of ink flying in the bubble jet recording system will be described referring to Figs. 17A to 17G. In a steady state, the surface tension and the external pressure of ink 20 filled in the nozzle 209d are kept in an equilibrium on the discharge port surface as shown in Fig. 17A. To fly the ink 20 in this state, energize the electric heat converter 209b within the nozzle 209d to rapidly rise the temperature of the ink within the nozzle 209d in excess of neutral boiling. Then the ink adjacent to the electric heat converter 209b is heated to produce microbubbles (bubbles) as shown in Fig. 17B, and the ink in the heated portion concerned vaporizes to cause film boiling, and then the bubble 21 rapidly grows as shown in Fig. 17C. When the bubble 21 grows to the maximum as shown in Fig. 17D, an ink drop 22 is pushed out from the discharge port within the nozzle 209d. Then, when energization of the electric heat converter 209b is finished, the grown bubble 21 is cooled by ink 20 within the nozzle 209d, shrinks as shown in Fig. 17E, and the ink drop flies from the discharge port by the growth and shrinkage of this bubble. Further, as shown in Fig. 17F, ink comes into contact with the electric heat converter 209b surface to suddenly cool, and the bubble 21 disappears or shrinks into a negligible small volume. When the bubble 21 shrinks, ink is fed into the nozzle 209d from the common liquid chamber 209g due to the capillary phenomenon as shown in Fig. 17G in preparation for the next energizing. Accordingly, the carriage mounted with such a recording head is reciprocated, and at the same time, the electric heat converter 209b is energized in accordance with a picture signal by synchronizing with the reciprocation to record an ink image on a recording sheet. As the configuration of the recording means, configurations disclosed in U.S. Patent No. 4,558,333 specification, Japanese Laid-Open Patent Publication No. 59-123670, etc. which are located in an area, in which a heat operating portion bends, can also be adopted in addition to the above-mentioned combination of the discharge port, liquid path and electric heat converter. Also, for the above-mentioned recording means, ink may be fed into the recording head from an ink cartridge loaded in the recording apparatus, and also a replaceable type recording head may be used in which an ink receiving chamber is provided within the recording head and the recording head is replaced when ink runs short in the ink receiving chamber. As to the form of the recording apparatus according to the present invention, it is used as an image output terminal (printer) for information processing equipment such as computers, and, in addition, as a copying apparatus in combination with a reader, etc., further as a facsimile apparatus having a transmitting and sending function, etc. Although a recording head for recording by using the ink jet method was used in this embodiment, the present invention is not limited to this, but any recording head for recording by using various methods such as the thermography, thermal transfer method, wire dot recording method, or electrostatic recording method may be used, of course. In the above-mentioned embodiment, control of a step motor for driving a serial recording head was described, but the present invention is not limited to this. Also in the case of a printer for recording in units of lines using a line type thermal head, etc. as the printing head, for example, it is possible to eliminate uneven carrying of a recording sheet in order to improve the recording quality by using a step motor for a sheet feed motor for carrying a recording sheet and by providing the same carrying control as in this embodiment. According to the present invention, as mentioned above, when accelerating a motor for carrying the recording means or recording medium, it is possible to reduce the speed variation and vibration of the motor by driving the motor with a period relating to the mechanical time constant for the corresponding carrying mechanism in accordance with the motor rotary speed.

Claims: A recording apparatus for moving a recording head (104, 209) to scan for recording, comprising a carriage driving system consisting of a carriage (105, 206) for mounting said recording head (104, 209), a stepping motor (106, 201) for moving said carriage (105, 206), a driver (107) for switching the exciting current to be fed to the coil (134, 135) of said stepping motor (106, 201) in accordance with a pulse signal (25), and a control means (101) for generating said pulse signal (25) to instruct said driver (107) to drive said stepping motor (106, 201), characterized in that said control means (101) is adapted to judge during acceleration whether or not the rotary speed of said stepping motor (106, 201) exceeds a specified value, wherein the interval between the pulses of said pulse signal (25) is set to be shorter than a mechanical time constant of said carriage driving system when said rotary speed of said stepping motor (106, 201) is less than said specified value, and wherein the interval between the pulses of said pulse signal (25) is set to be longer than said mechanical time constant of said carriage driving system when said rotary speed of said stepping motor (106, 201) exceeds said specified value. An apparatus according to claim 1, characterized in that said control means (101) has a timer (114) which is capable of determining the interval between the pulses of said pulse signal (25), wherein the period of said timer (114) is set in accordance with whether or not the rotary speed of said stepping motor (106, 201) exceeds said specified value. An apparatus according to claim 1 or 2, characterized in that said specified value for the rotary speed of said stepping motor (106, 201) amounts to almost half of the target rotary speed. An apparatus according to one of the preceding claims, characterized in that said control means (101) has a ROM (112) to control the apparatus, and that the output timing for said pulse signal (25) is stored in said ROM (112) in order to switch the exciting current of said stepping motor (106, 201). An apparatus according to one of the preceding claims, characterized in that said carriage driving system further comprises a detecting means (127 - 129) for detecting whether or not said carriage (105) is at its home position, said detecting means (127 - 129) being capable of generating a detection signal for initializing said control means (101), when said carriage (105) has been detected at its home position, wherein said control means (101) further comprises a counter (116) for detecting the position of said carriage (105) by counting the pulses of said pulse signal (25), and wherein said control means (101) is adapted to judge on the basis of the count value of said counter (116) whether or not the rotary speed of said stepping motor (106) exceeds said specified value when accelerating until said carriage (105) reaches a record-starting position. An apparatus according to one of the preceding claims, characterized in that said carriage driving system further comprises a guide member (252) for guiding said carriage (206) when it is moved, and an elastic member (217, 218) provided between said carriage (206) and said guide member (252), said elastic member (217, 218) being adapted to press said carriage (206) in a direction which keeps the latter away from said guide member (252). An apparatus according to claim 6, characterized in that said elastic member (217) is coated with a solid lubricant. An apparatus according to claim 6, characterized in that said elastic member (218) is formed integrally with said carriage (206). An apparatus according to one of the preceding claims, characterized in that said recording head (104) is an ink jet recording head. An apparatus according to claim 9, characterized in that said recording head (104) is an ink jet recording head which is capable of recording by discharging ink by the growth of a bubble.

Inventors: ITO NORIAKI C O CANON KABUSHIK, NAGOSHI SHIGEYASU C O CANON KA, YOSHIMURA SHIGERU C O CANON KA, ITO, NORIAKI, C/O CANON KABUSHIKI KAISHA, NAGOSHI, SHIGEYASU, C/O CANON KABUSHIKI KAISHA, YOSHIMURA, SHIGERU, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: B41J19
IPC codes: B41J19, H02P8