JP2009297956A - Recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that vibrations and noises are easy to be generated as the minimum value of the electric current energized into a motor is restricted by a counter-electromotive force of a motor when the speed of a carriage is decreased in a recording apparatus. <P>SOLUTION: When either one or both of the amount of movement and a target track of the carriage are larger than a specified threshold value by the absolute values when the speed of the carriage is decreased, an inputting signal to a motor driver is held at a specified value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a recording apparatus such as an ink jet printer. In particular, the present invention relates to driving of a carriage equipped with a recording head.

  With the remarkable development of electronics technology, the processing power of computers has made great progress. In particular, in order to perform color image processing, a large amount of data must be processed in a short time. Conventionally, there has been a difficulty in processing speed, but in recent years, the improvement in computer capabilities has made such color image processing very common.

  In addition, the range of use of recording devices for outputting color images is rapidly expanding. In place of conventional photographic printing, a scene in which a color image is output using a recording apparatus typified by an ink jet printer is increasing. The range of use of inkjet printers is expanding from small business cards to large poster sizes larger than B0. In addition, with the widespread use of recording apparatuses, demands for image quality improvement and throughput improvement for the apparatuses are increasing. Generally, in a recording apparatus, printing is performed while a recording head is scanned with respect to a recording medium. For this reason, higher precision and higher speed are required for the carriage on which the recording head is mounted.

  In response to such a demand, the recording apparatus employs a so-called servo mechanism that detects the amount of movement of the carriage with an encoder and drives the carriage according to a difference between a separately determined target amount of movement and the amount of movement. Has been. When print data is received from an external computer, the carriage is driven by the servo mechanism, and printing is started when a certain scanning speed is reached. The carriage stops when recording of recording data corresponding to one scan is completed. Further, when there is recording data, carriage driving and recording are repeated.

  If such a carriage drive pattern is schematically shown, a pattern as shown in FIG. 5 is typical. First, smooth acceleration is performed so as not to generate vibration and noise in the acceleration section. Next, in the constant speed section, recording is performed while the carriage is driven at a predetermined scanning speed. In the deceleration zone after the end of recording, the carriage is quickly decelerated and stopped while avoiding the generation of vibration and noise, as in the acceleration zone. That is, the servo mechanism operates so as to maintain constant velocity in the constant velocity section, and so that vibration and noise are not generated in the acceleration section and the deceleration section due to a rapid change in speed and driving state.

  One of the causes of vibration and noise is that the mechanical natural vibration of the recording apparatus is excited by driving the carriage. It is important to exclude the component corresponding to the natural frequency from the frequency component included in the driving of the carriage, that is, the frequency component of the acceleration generated in the carriage or the same component of the driving force applied to the carriage. In general, mechanical natural vibration exists in a high frequency band of a certain level or more. Therefore, it is effective to limit the frequency band for driving the carriage. Another cause is the amount of change in acceleration, that is, the size of jerk. By limiting the maximum value of jerk, the generation of vibration and noise can be avoided.

  In the prior art, there is a known example that considers avoidance of vibration and noise in the generation of the drive pattern. A frequency band restriction is provided on the target trajectory of position, velocity, and acceleration, and a maximum value restriction is provided on jerk, which is a derivative of the target trajectory of acceleration (Patent Document 1).

However, the drive pattern is an input given to the servo mechanism. The output corresponds to the actual position, speed, and acceleration of the controlled object, and vibration and noise are inevitable unless the output is restricted in the same way as the input. There are no known techniques for this.
JP-A-8-286761 (FIG. 1)

  As described above, the carriage servo mechanism as found in the conventional recording apparatus has a problem that vibration and noise are likely to occur during acceleration or deceleration. This problem is particularly noticeable during deceleration. This is because it is difficult to appropriately control the current of the motor, which is an actuator, during deceleration.

  In general, a PWM motor driver is employed in consumer equipment or industrial equipment represented by a recording device. The operation of the motor driver of the same system and the direction of the motor current will be described with reference to FIG. FIG. 6A shows the case of energization in the positive direction. Here, the case where the motor current and the counter electromotive force Ve are in the opposite directions is called forward energization for convenience. This corresponds to acceleration of the carriage or scanning at a constant speed. The motor 102 is driven by output transistors 101a, 101b, 101c, and 101d. In the forward direction energization operation, as the upper PWM, the output transistor 101a is switched, the output transistors 101b and 101c are off, and the output transistor 101d is on. The magnitude of the motor current is determined according to the back electromotive force Ve and the PWM duty which is an input signal to the motor driver.

  In contrast, FIG. 6B shows the case of reverse energization or short brake. This corresponds to the case where the carriage is decelerated. The reverse direction energization refers to the case where the motor current and the back electromotive force Ve are in the same direction for convenience. The states of the output transistors 101a, 101b, 101c, and 101d are that the output transistor 101c is switched, the output transistors 101a and 101d are off, and the output transistor 101b is on. Alternatively, a motor current flows in the direction of decelerating the carriage even with a short brake. When the short brake is set, the states of the output transistors 101a, 101b, 101c, and 101d are on, the output transistors 101a and 101c are on, and the output transistors 101b and 101d are off. The motor current direction is the same for both reverse energization and short brake.

  In order to smoothly decelerate the carriage, the motor current must be controlled to a desired state. However, the problem in the case of reverse energization or short brake in FIG. 6B is that the minimum value of the motor current is limited by the back electromotive force Ve. Of the motor current, the component due to the back electromotive force Ve is uncontrollable. Therefore, the braking torque for deceleration is limited to the minimum value by the back electromotive force Ve, and a minute braking torque cannot be generated. If such a disadvantage is ignored and the servo mechanism is operated, a sudden change in the motor current occurs during deceleration, and vibration or noise occurs in the carriage.

  FIG. 7 shows a typical case in which vibration or noise is generated when the carriage is decelerated in the recording apparatus according to the prior art. The carriage speed and motor current are shown in the time axis response and only in the deceleration zone. The acceleration section and the constant speed section are not shown. In FIG. 7A, the motor current is controlled by the operation of the servo mechanism so that the speed target trajectory indicated by the broken line and the speed indicated by the solid line coincide. If the motor current can be controlled to an arbitrary state, the speed and the speed target trajectory can be completely matched. FIG. 7B shows the motor current. Since the braking torque is applied and the carriage is quickly decelerated, as described above, the motor driver is in a reverse energization state or a short brake state. In this state, the component due to the counter electromotive force in the motor current is uncontrollable, and the motor current cannot be controlled to an arbitrary value. The minimum braking torque for deceleration is limited by the back electromotive force. In order to obtain a braking torque smaller than this, the energization direction of the motor driver can only be switched to accelerate the carriage. Therefore, in the deceleration zone, the energization direction of the motor driver is frequently switched and a sudden change in the motor current occurs. A large jerk is given to the carriage, and vibration and noise are excited.

  The counter electromotive force gives discontinuity to the servo mechanism. FIG. 8 illustrates this situation, and schematically shows the relationship between the PWM duty input to the motor driver and the motor current. The sign is assumed that the PWM duty and the motor current are positive in the acceleration section or the constant speed section. The energization direction of the motor driver is switched according to the sign of the PWM duty. Then, due to the back electromotive force, a point where the change of the motor current becomes steep with respect to the PWM duty can be made, such as from point A to point B or from point B to point A in FIG. This leads to a sudden change in braking torque, and vibration and noise are excited in the carriage.

  The present invention has been made in view of the above circumstances. That is, an object of the present invention is to provide a carriage servo mechanism that can avoid generation of vibration and noise during deceleration in a recording apparatus. Another object of the present invention is to provide a recording apparatus that is excellent in the reproducibility of the operation of the servo mechanism and the durability of the carriage by avoiding the generation of vibration and noise.

  In order to solve the above problems, a recording apparatus according to the present invention described in claim 1 is a recording apparatus that performs recording by moving a recording head relative to a recording medium, and the recording head is mounted thereon. A carriage, a motor that applies thrust to the carriage, a movement amount detector that detects a movement amount of the carriage, a target trajectory generator that gives a target trajectory to the movement amount of the carriage, a motor driver that drives the motor, A control loop that calculates an input signal to the motor driver according to the movement amount and the target trajectory, and when the carriage decelerates, either or both of the movement amount and the target trajectory are less than a predetermined threshold value. If the absolute value is too large, the recording loop operates so that the control loop holds the input signal to the motor driver at a predetermined value.

  The recording apparatus according to the second aspect of the present invention is a recording apparatus in which the movement amount detector detects the speed of the carriage, and the target trajectory generator generates a speed target trajectory.

  The effects of the present invention are as follows.

  First, vibration and noise can be suppressed by the carriage of the recording apparatus. Since the carriage can be decelerated promptly and smoothly, the throughput of the recording apparatus can be improved. In particular, the reproducibility of driving during deceleration increases, contributing to stabilization of throughput. Since unnecessary vibrations are not excited, the durability of the mechanism is improved.

  Moreover, in a recording apparatus that is a consumer device or an industrial device, a PWM system is generally employed as a motor driver. If a linear motor driver is employed, the motor current can be controlled linearly, which greatly contributes to suppression of vibration and noise. However, it is well known that the power efficiency decreases in the linear method, and it is essential to increase the capacity of the driver and to take measures against heat. This directly leads to an increase in the cost of the recording apparatus. The present invention assumes a PWM motor driver. Since the vibration and noise can be suppressed by this method, the cost of the recording apparatus can be prevented from increasing.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 4 is an oblique projection showing the carriage 1 and a mechanism for driving the carriage 1. A carriage 1 on which a recording head is mounted is guided by two guide shafts 2 and reciprocates in the scanning direction. The belt 3 is fixed to the carriage 1 via a belt holder 4. The belt 3 is suspended by the pulley 6 and the idle pulley 7 without slack. The pulley 6 and the idle pulley 7 are respectively disposed at both ends of the carriage 1 in the scanning direction. A motor 5 that is an actuator is connected to the pulley 6. The driving force generated by the motor 5 is transmitted as a thrust to the carriage 1 via the pulley 6, the idle pulley 7 and the belt 3. That is, the rotational motion of the motor 5 is converted into the translational motion of the carriage 1 through these mechanisms. The encoder 8 is a detector for detecting the amount of movement of the carriage 1 in the scanning direction.

  FIG. 1 is a block diagram showing a servo mechanism of a carriage 1 according to the present invention. When the carriage 1 is scanned with respect to the recording medium, information on the position and speed of the carriage 1 is required. The displacement and speed are extracted based on the signal from the encoder 8. The operation of the speed detector 13 generates speed information from the output of the encoder 8. The operation is known, and for example, the time width of the pulse train output from the encoder 8 is measured or the amount of change per unit time of the pulse train is calculated. The operation of the position detector 14 is also known. The position information is obtained by counting the pulse train output by the encoder 8.

  The target trajectory generator 9 outputs a time axis profile when the carriage 1 scans the recording medium in the form of a position target trajectory, a speed target trajectory, and an acceleration target trajectory. These quantities have a differential and integral relationship with each other. The position information output from the position detector 14 is subtracted from the position target trajectory output from the target trajectory generator 9 and guided to the position compensator 10. The speed compensator 11 derives a difference value between the speed and the speed target trajectory and an output signal of the position compensator to generate a compensation value. Such a double loop of position and speed is a conventional means of a servo mechanism. Normally, the position compensator performs proportional operation, and the speed compensator performs proportional + integral operation.

  The switcher 12 operates to appropriately switch the state of the motor driver 15 for the purpose of avoiding vibration and noise of the carriage 1 during deceleration. As described with reference to FIG. 8, when the energization direction of the motor driver 15 is switched, a large discontinuity occurs in the motor current due to the influence of the counter electromotive force. In general, when the motor 5 is decelerated or stopped along a temporal target profile, switching occurs in the energization direction of the motor driver 15. Since the back electromotive force is proportional to the rotational speed of the motor 5, the higher the speed of the carriage 1, the larger the change in motor current when the energization direction of the motor driver 15 is switched, and the braking torque transmitted to the carriage 1. The change is also big. This means that the jerk of the carriage 1 is large. Jerk leads to noise. Therefore, if the energization direction is frequently switched when the speed of the carriage 1 is high, vibration and noise are generated in the carriage 1. The essence of the present invention is to maintain the input signal to the motor driver 15 at a predetermined value when the speed of the carriage 1 is high during deceleration, thereby avoiding frequent switching of the energization direction. This avoids the vibration and noise of the carriage 1.

  The operation of the switch 12 will be described with reference to the flowchart of FIG. Since the carriage 1 is scanned in a reciprocating manner, state quantities such as a movement amount and a compensation value have positive and negative signs corresponding to the reciprocating operation. In the figure, a positive sign is used as a reference for the sake of brevity. That is, when the respective state quantities are positive, the carriage 1 is driven in the scanning direction. As a main operation of the switching device 12, when the carriage 1 is in the deceleration zone and the speed or the speed target trajectory is larger than the threshold value, the state of the motor driver 15 is set to the short brake so that the carriage 1 is decelerated. The braking torque is applied. In order to avoid frequent switching of the energization direction, the short brake state is always used.

  In FIG. 2, first, the processing block 201 determines whether or not the carriage 1 is in the deceleration zone. The scanning state is divided into an acceleration section, a constant speed section, and a deceleration section. In this embodiment, when the acceleration target trajectory output by the target trajectory generator 9 is negative, it is determined that the vehicle is in the deceleration zone. When it is in the acceleration section or the constant speed section, the processing block 205 and subsequent steps are executed. The PWM duty is set in accordance with the absolute value of the compensation value output from the speed compensator 11, and the sign of the compensation value is determined in the processing block 206. When the compensation value is positive, the motor driver 15 is energized in the forward direction, and when negative, it is energized in the reverse direction.

  If it is determined in the processing block 201 that the vehicle is in the deceleration zone, the processing is further branched by the processing block 203 based on the speed or the speed target trajectory. When the speed is larger than a predetermined speed threshold or the speed target trajectory is larger than the speed threshold, the back electromotive force of the motor 5 is large, and if the energization direction of the motor driver 15 is frequently switched, the carriage 1 vibrates. It is judged that noise is generated. Therefore, the motor driver 15 is always set to the short brake regardless of the sign and absolute value of the compensation value. That is, when in the deceleration zone and the speed or speed target trajectory is larger than the predetermined speed threshold, the setting of the motor driver 15 is always a short brake and the switching of the energization direction does not occur. In the short brake state, the braking torque is determined by the counter electromotive force, and the braking torque is not corrected according to the deviation in the position and speed of the carriage 1. In general, since the position compensator 10 or the speed compensator 11 includes an integration operation, the process 204 executes an integration reset for the purpose of preventing windup of the integration operation.

  The operation flow of the switch 12 is as described above. Returning to the block diagram of FIG. 1, the switch 12 determines an input signal to be given to the motor driver 15 in accordance with state quantities such as a speed threshold, an acceleration target trajectory, a speed target trajectory, a speed, and a compensation value. When the speed compensator 11 includes an integration operation, an integration reset is executed to prevent windup.

  FIG. 3 is a time axis response showing the operation of the recording apparatus according to the present invention. The speed of the carriage 1, the PWM duty given to the motor driver, and the motor current of the motor 5 are shown on the same time axis in order from the top of the figure. The shaded part in the figure is in the deceleration zone and the speed is greater than the speed threshold. At this time, the motor driver 15 is held in a short brake state. Since the motor current is determined by the back electromotive force of the motor 5, the motor current and the speed are similar and have a smooth waveform. If the speed is smaller than the speed threshold even in the deceleration zone, the servo mechanism operates in accordance with the position and speed deviation. At this time, the energization direction of the motor driver 15 can be switched frequently, but since the speed is low and the carriage 1 is located near the position target track, the amount of change in the motor current is also small. Therefore, it is possible to avoid occurrence of vibration and noise of the carriage 1 in the deceleration zone.

  In the embodiment, the case where the motor driver 15 is in a short brake state is disclosed, but the embodiment of the present invention is not limited to such a case. The essence of the present invention is to keep the input signal to the motor driver 15 at a predetermined value when the speed of the carriage 1 is high in the deceleration zone, thereby avoiding frequent switching of the energization direction. Therefore, not only the short brake, but the same effect can be obtained even if, for example, the energization direction is reversed and the PWM duty is fixed to a predetermined value. Further, in order to determine that the carriage 1 is in the deceleration zone, the sign of the acceleration target trajectory is used as a criterion in the embodiment, but other signals such as a position target trajectory may be used. Thus, the present invention can be implemented in various forms.

1 shows a preferred embodiment of the present invention. The figure which shows the flowchart of embodiment. 2 is a diagram illustrating the operation of a carriage according to the present invention. The drawing which shows the mechanical structure of a carriage. The drawing which shows the typical drive pattern of a carriage. Drawing which shows the energization direction of a motor driver. FIG. 6 is a diagram illustrating the operation of a carriage according to the prior art. The figure which shows the input / output characteristic of a motor driver typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Carriage 2 Guide shaft 3 Timing belt 4 Belt holder 5 Motor 6 Pulley 7 Idle pulley 8 Encoder 9 Target trajectory generator 10 Position compensator 11 Speed compensator 12 Switcher 13 Speed detector 14 Position detector 15 Motor driver 101a, 101b , 101c, 101d Output transistor 102 Motor 103 Current detection resistor 201-208 Processing block

Claims (2)

In a recording apparatus that performs recording by moving a recording head relative to a recording medium,
A carriage on which the recording head is mounted; a motor that applies thrust to the carriage; a movement amount detector that detects a movement amount of the carriage; and a target trajectory generator that provides a target trajectory with respect to the movement amount of the carriage; A motor driver for driving the motor, and a control loop for calculating an input signal to the motor driver according to the movement amount and the target trajectory,
When the carriage decelerates, if one or both of the movement amount and the target trajectory are larger in absolute value than a predetermined threshold, the control loop holds the input signal to the motor driver at a predetermined value. Recording device that operates to do.   The recording apparatus according to claim 1, wherein the movement amount detector detects a speed of the carriage, the target trajectory generator generates a speed target trajectory, and the threshold is a threshold relating to speed.

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