JP2007253330A - Positioning control device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stable, highly precise, inexpensive positioning control device by a constitution wherein a position detector is disposed away from a transmission mechanism section in order to suppress a position detection error generated by twist or the like of the transmission mechanism section with respect to a mechanism having a large load in a transmission mechanism system having a low rigidity. <P>SOLUTION: This positioning control device comprises the transmission mechanism section for transmitting a drive force of a motor 201, a movable section driven by the transmitted drive force of the motor, a positioning mechanism having the position detector, and a control mechanism having a driver section for driving the motor according to an output of a control computing section by feeding back the output of the position detector. The position control device performs controlling of positioning to a target position. The position detector is disposed on a position away from a place where the transmission mechanism section is attached to the movable section and the control computing section takes account of a twist characteristic. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a highly accurate positioning control device in a mechanism having low rigidity and a large friction load, and includes a precision feeding mechanism that repeats step feed, a sub-scanning positioning control device for an ink jet printer, an XY stage positioning control device, It can be used for a belt feeding mechanism or the like.

One example of the prior art related to this type of ultra-precision positioning device is described in Japanese Patent Publication No. 7-122830, which is based on coarse / fine motion control in consideration of the elastic characteristics of the rolling guide in a linear motion stage. Realized ultra-precision positioning.
Japanese Patent Publication No. 7-117855 describes a positioning control method for a moving body, which changes a transfer function of a control loop in consideration of elastic characteristics according to a moving distance.

  Japanese Patent Application Laid-Open No. 2002-248822 describes an invention for improving the rotation accuracy of a conveyance roller. This is a method in which a code wheel is mounted on a conveyance roller shaft driven via a timing belt and a sensor reading is performed. The direction is configured to be perpendicular to the direction of the tension that the conveyance roller receives from the timing belt, and the rotation accuracy of the conveyance roller is improved.

The following prior arts have already been filed and published.
In other words, this is a method in which two encoders with different resolutions are provided and an encoder with a low resolution is corrected with an encoder with a high resolution, and the mechanism is applied to a recording paper transport device (Japanese Patent Laid-Open No. 2005-319739).

  Further, as a patent application that has not been published yet, there is a belt conveyance device that includes a belt mark sensor (linear encoder) on an endless belt and a rotation angle sensor (rotary encoder) on a roller that supports the endless belt ( Japanese Patent Application No. 2004-344666), in which the belt conveying device is applied to a paper conveying device of an inkjet printer or a multifunction printer.

  Furthermore, there is an invention that realizes high-accuracy positioning by providing a control method that takes into account the torsion of a minute region of the transmission system (Japanese Patent Application No. 2005-258538), and this positioning device is an inkjet printer or multifunction printer. This is applied to the paper transport apparatus.

[Problems of the prior art]
The present invention is an invention of a precision feed mechanism that repeats step feed, and in particular, is an invention that can be applied to a positioning device of a paper transport device of an inkjet recording apparatus that is a high-precision positioning mechanism considering low cost. In the field of the ink jet recording system, the ink is changed from a dye system to a pigment system in order to improve the light resistance and deterioration with time of the ink, and the viscosity of the ink is increasing. Although the blur on the recording paper has been drastically reduced due to the increase in viscosity, conversely, the poor positioning accuracy of the ink droplet landing position on the recording paper can be clearly seen (white stripes, black stripes, banding). In particular, since the contribution ratio of stop position accuracy during conveyance of recording paper in the sub-scanning direction is large, it has become an indispensable technical problem.

  In the conventional sub-scanning recording paper transport mechanism of the ink jet recording system, a transport method using a grindstone transport roller or a transport belt has been generally used. For the feed amount control, a code wheel is installed on the transport roller shaft, and this value is measured by an encoder sensor. In general, the reading control is performed by the above method. For example, Japanese Patent Laid-Open No. 2002-248822 discloses a configuration in which a conveyance roller and a discharge roller are arranged on the upstream side and the downstream side of a platen to convey recording paper in the sub-scanning direction, and a code wheel is installed on the conveyance roller shaft. An apparatus that controls the conveyance of recording paper by reading this value with an encoder sensor is disclosed.

  In the sub-scanning recording paper transport mechanism of the ink jet recording system, positioning accuracy of several μm is required for high image quality, and speeding up of the line feed time is also required for improving productivity. However, since it is an inexpensive product, it is difficult for the drive system to ensure sufficient rigidity to satisfy the above performance. In addition, there are nonlinear characteristics due to sliding resistance and elastic deformation, and the required accuracy cannot be achieved by general linear control.

For example, in the case of a mechanism for driving a recording paper conveyance shaft from a motor via a timing belt and a pulley, the load resistance of a portion (grindstone conveyance roller or conveyance belt) on the recording paper conveyance shaft that conveys the recording paper is large. The twist of a pulley and a recording paper conveyance axis | shaft and the phenomenon in which the rubber layer on an axis | shaft elastically deforms generate | occur | produces. As a result, there is a problem that even if positioning is performed using an encoder on the pulley, the position on the recording paper transport shaft does not become the target position.
Furthermore, when the load resistance is large and the rigidity is low, mechanical resonance due to the control system is likely to occur, and the proportional gain of the control system cannot be increased. For this reason, a method of suppressing a stationary position deviation using an integrator or the like is common, but there is a problem that it takes time to suppress the position deviation.

  In addition to the paper transport device described above, in an inexpensive XY stage used in a production device, an inspection device, etc., a rotary motor with an encoder attached coaxially, a ball screw that transmits the driving force of the rotary motor and moves the carriage, In many cases, it is composed of a carriage and a rolling guide for restraining the carriage. In such a configuration, when the load between the rolling guide and the carriage is large and the rigidity of the ball screw or the like as the drive transmission unit is low, the transmission system is twisted and the linear motion guide unit is elastically deformed. For this reason, even if positioning control for feeding back the value of the encoder attached to the motor shaft is performed and the value of the encoder indicates the target position, the carriage is not necessarily stopped at the target position.

  Further, similarly to the sub-scanning recording paper transport mechanism of the ink jet recording method, when the load resistance is large and the rigidity is low, mechanical resonance due to the control system is likely to occur, and the proportional gain of the control system cannot be increased. For this reason, a method of suppressing a stationary position deviation using an integrator or the like is common, but there is a problem that it takes time to suppress the position deviation.

An invention for positioning at a target position with high speed and high accuracy is described in Japanese Patent Publication No. 7-122830, and the present invention mainly relates to a nanometer order ultra-precision positioning stage for precision technology such as semiconductor manufacturing and laser optics. It is.
A typical ultra-precision positioning stage is composed of an air bearing, a vacuum lock, a fine movement spring, a linear motor, a coarse movement controller, and a fine movement controller. On the other hand, in the ultraprecision positioning device described in Japanese Patent Publication No. 7-122830, the air bearing, vacuum lock, and fine movement spring are replaced with rolling guides, and the coarse movement controller, fine movement controller, and switching method are devised. Thus, a high-speed and high-precision precision positioning device with a simple configuration is realized.

  In the above prior art, the linear motor is directly attached to the carriage of the stage, and the position of the carriage can be directly detected by providing the carriage with a position detection unit. For this reason, an error due to the rigidity of the transmission system and the movable part, which is one of the above problems, does not occur. Therefore, if the invention of the above prior art is simply applied to a positioning device having a transmission system with low rigidity, the value of the encoder and the displacement amount of the movable part cannot be matched.

  In general, in order to make the encoder value coincide with the displacement amount of the movable part, the carriage is equipped with a linear motor as in the stage described in Japanese Patent Publication No. 7-122830, and the position of the carriage can be detected directly. It is necessary to sufficiently improve the rigidity of the transmission mechanism system against the elastic deformation caused by the load or the driving force of the motor.

[Problems of the prior art]
In order to correctly detect the position of the movable part and perform high-precision positioning, the invention of Japanese Patent Application No. 2004-141094 (Japanese Patent Laid-Open No. 2005-319739) and the invention of Japanese Patent Application No. 2004-344666 are provided on an endless belt. These encoders are a method of arranging encoders, but these prior arts are to arrange a tape-like encoder on an endless belt, and for that purpose, a process of processing the encoder into a tape and pasting it with high accuracy is required Therefore, the cost increases. Further, since the seam is generated when the tape has an end, a method for processing the seam of the encoder is necessary. Even when the encoder pattern is directly processed on the endless belt, a surface treatment of the endless belt and a process of processing the encoder pattern one by one are required, leading to an increase in cost. Further, in order to increase the detection accuracy, it is necessary to keep the distance between the encoder pattern and the encoder sensor within a predetermined range. However, since the belt is likely to swing, the detection accuracy may be lowered. In addition, since these inventions use two encoders and complement the encoders on the endless belt with the rotary encoders, there is a high possibility that the detection accuracy will decrease.

Although not known, the invention of Japanese Patent Application No. 2005-258538 is intended to achieve highly accurate positioning by a control method that takes into account the torsion of a minute region of the transmission system. Since a certain encoder, for example, an encoder on a pulley, is used, the movement of the movable part, which is the final stage, is calculated based on displacement data detected in advance. Therefore, if the characteristics such as the rigidity of the transmission system change due to the temperature characteristics or the like, a positioning error may occur.
Japanese Examined Patent Publication No. 7-122830 Japanese Patent Publication No.7-1117855 JP 2002-248822 A JP 2005-319739 A

[Problems of the invention of claim 1]
The object of the invention of claim 1 is to separate the position detector from the transmission mechanism portion in order to suppress a position detection error caused by torsion or the like of the transmission mechanism portion with respect to a mechanism having a low rigidity of the transmission mechanism system and a large load. Thus, a stable, highly accurate, and inexpensive positioning control device is provided.
[Problem of invention of claim 2]
An object of the invention of claim 2 is to provide a positioning control device provided with a control mechanism for positioning the configuration of claim 1 with high accuracy.
[Problem of invention of claim 3]
An object of the invention of claim 3 is to provide a controller for performing positioning with high accuracy and stability.
[Claim 4 is an object of the invention]
An object of the invention of claim 4 is to provide stable switching between the first control step and the second control step.
[Problem of invention of claim 5]
An object of the invention of claim 5 is to reduce the load on the control operation unit and to use an inexpensive operation unit for control by causing a higher-order operation unit to execute the operation of each step. .
[Problems of invention of claim 6]
An object of the invention of claim 6 is to make it possible to reduce the computation load of the higher-order computing unit by causing the computing unit of the control computing unit to execute the computation of each step.
[Problem to the Invention of Claim 7]
By mounting the positioning control device according to any one of claims 1 to 6, an inexpensive, stable and highly accurate image forming apparatus is provided.

[Means for Solving the Invention of Claim 1]
The solving means of the invention of claim 1 is as follows.
A single motor, a transmission mechanism that transmits the driving force of the motor, a movable portion that is driven by transmission of the driving force of the motor, a positioning mechanism that includes a position detector, and an output of the position detector are fed back. A low-stiffness composed of a control calculation unit that performs a predetermined calculation and a control mechanism that includes a driver unit that drives the motor based on the output of the control calculation unit, and the transmission mechanism unit or the movable unit exhibits torsional characteristics In a positioning control device that is configured from a member and performs positioning control at a target position,
A positioning control device comprising: the position calculation unit disposed at a position away from a place where the transmission mechanism unit is attached to the movable unit, and the control calculation unit considering the torsion characteristics.
The above-mentioned “transmission mechanism” means a speed reduction mechanism composed of gears, pulleys, timing belts, etc., and “the place where the transmission mechanism is attached to the movable part” means that the movable part is supported by the rotary part. In addition, “a position away from the place” means a position away from the place in the direction of the axis of the rotating body, and “a position detector on the movable part. For example, when the timing pulley is fixed to one end of the driving roll of the electrostatic adsorption belt of the recording paper transport device, the position detector is fixed to the other end. To do.

[Means for Solving the Invention of Claim 2]
The solving means of the invention of claim 2 is as follows.
The positioning control device according to claim 1,
A control controller including a first controller that takes into account characteristics when the movable part largely moves; and a second controller that takes into account characteristics of a minute region;
A first control step for setting a target position and performing positioning by the first controller; and a second control step for performing positioning by the second controller when a predetermined positional deviation is reached with respect to the target position. A positioning control device characterized by that.
The first controller performs a coarse movement operation that brings the movable part close to the target position at a high speed, and the second controller performs a fine movement operation that positions the movable part at the target position.

[Solution to Invention of Claim 3]
The solving means of the invention of claim 3 is as follows.
The positioning control device according to claim 2, wherein the second controller is configured in consideration of the fact that the order of the control target is larger than that of the first controller.
[Means for Solving the Invention of Claim 4]

The solution of the invention of claim 4 is as follows.
The positioning control device according to claim 2, wherein hysteresis is given to a predetermined position deviation for switching between the first control step and the second control step.
[Means for Solving the Invention of Claim 5]

The solving means of the invention of claim 5 is as follows.
3. The positioning control apparatus according to claim 2, wherein the first control step and the second control step are switched by a computing unit at a higher level.
[Means for Solving the Invention of Claim 6]

The solving means of the invention of claim 6 is as follows.
3. The positioning control device according to claim 2, wherein the first control step and the second control step are switched by a calculator that constitutes the control calculation unit.
[Means for Solving the Invention of Claim 7]

The solving means of the invention of claim 7 is as follows.
An image forming apparatus comprising the positioning control device according to claim 1.

The effects of the present invention are as follows.
[Effect of the invention according to claim 1]
By separating the position detector from the transmission mechanism for a mechanism with low transmission mechanism rigidity and large load, it is possible to directly measure the position of the movable part that does not include position detection errors caused by torsion of the transmission mechanism. become. As a result, it is possible to provide a stable, highly accurate and inexpensive positioning control device mechanism.
Further, since the transmission mechanism part or the movable part is composed of a low-rigidity member exhibiting torsional characteristics, it can be manufactured at low cost.
Furthermore, by providing the control calculation unit considering the torsional characteristics, it is possible to perform highly accurate positioning with an inexpensive configuration without changing the configuration.
Compared to the conventional positioning control device, it is possible to cope with the use of low-rigidity members, the change of the position detector mounting position, the software of the control calculation unit, etc. Can be provided.

[Effect of the invention according to claim 2]
By providing two types of controllers and two types of control steps in the configuration of claim 1, it is possible to provide a positioning control device capable of highly accurate positioning.

[Effect of the invention according to claim 3]
By preparing a controller that matches the mechanical characteristics of the control step, high-accuracy positioning is possible.

[Effect of the invention according to claim 4]
By providing hysteresis at the switching point between the first control step and the second control step, it is possible to switch the step smoothly and stably.

[Effect of the invention according to claim 5]
It is possible to reduce the load of sequence operation of the control operation unit by causing the upper operation unit to execute the operation of each step. As a result, an inexpensive arithmetic unit for control can be used. In addition, since the control calculation unit can be made analog, the control calculation can be speeded up and the cost can be reduced.

[Effect of the invention according to claim 6]
By causing the calculation unit of the control calculation unit to execute the calculation of each step, the calculation load of the higher-level calculation unit can be reduced. As a result, the high-order computing unit can specialize in image processing and other operation computations.

[Effect of the invention according to claim 7]
By mounting the positioning control device according to the first to sixth aspects, an inexpensive, stable and highly accurate image forming apparatus can be provided.

Next, embodiments will be described with reference to the drawings.
FIG. 1 is a cross-sectional configuration diagram showing an example of an ink jet recording apparatus provided with a paper conveying apparatus according to the present invention. The ink jet recording apparatus 100 shown in this figure is configured as a copying apparatus with a scanner unit 30 disposed above a printer unit 50. A paper discharge unit 40 is formed between the scanner unit 30 and the printer unit 50.
The scanner unit 30 is provided with a scanning unit 32 below the contact glass 31 so that the scanning unit 32 can travel. The scanner unit 30 guides reflected light from a document illuminated by a light source to a CCD 33 via a mirror lens or the like, and reads a document image. Is done. A pressure plate 34 is provided above the contact glass 31 so as to be openable and closable.

  In the printer unit 50, a recording paper conveyance path from the paper feeding cassette 27 disposed below to the paper discharge unit 40 is formed as indicated by a one-dot chain line in the drawing, and a conveyance roller is provided at a predetermined position in the recording paper conveyance path. 25 is installed as appropriate. Reference numeral 24 denotes a paper feed roller, and reference numeral 26 denotes a paper discharge roller. A manual feed tray 28 is provided on the side of the apparatus, and recording paper is also fed from the manual feed tray 28 via a paper feed roller 29.

  The ink jet engine 20 includes a recording paper conveyance device 1. In this embodiment, a system for conveying the recording paper in the sub-scanning direction using an electrostatic adsorption belt is employed. The conveyance system using the electrostatic adsorption belt can feed the paper more stably than the conventional roller conveyance system. The carriage 21 positioned on the recording paper transport device 1 is mounted with a print head 22 and reciprocates in the main scanning direction (direction perpendicular to the drawing), and performs printing by ejecting ink droplets from the print head 22. The print head 22 has a four-head configuration of one head for each color of cyan (C), magenta (M), yellow (Y), and black (Bk). However, the number of heads is not limited to this, and a two-head configuration of one head with two colors may be used. Also, a line head that does not reciprocate in the main scanning direction may be used.

  In the ink jet recording apparatus 100 of this embodiment, each color ink cartridge 23 is mounted separately from the print head, and the ink in the cartridge 23 is supplied to the print head 22 via a supply tube (not shown). A system in which each color ink cartridge is mounted separately from the print head is a system suitable for business use because a large-capacity type cartridge corresponding to an increase in ink consumption accompanying an increase in printing speed can be used. However, the ink supply method may be a configuration in which the head and the cartridge are integrated.

FIG. 2 is a detailed view showing the configuration of the recording paper transport apparatus 1 in detail.
In FIG. 2, an electrostatic attraction belt 2 as a conveying means for conveying a recording sheet in the sub-scanning direction is formed in an endless loop shape and is stretched between a conveying roller 3 and a tension roller 4. A charging roller 5 for applying an electric charge to the electrostatic attraction belt 2, a neutralizing brush 6 for neutralizing the electrostatic attraction belt 2, and a cleaning blade 7 for cleaning the electrostatic attraction belt 2, respectively. It is in pressure contact with the outer peripheral surface. The charging roller 5, the charge eliminating brush 6 and the cleaning blade 7 are supported by the bracket 16. The bracket 16 is provided with a collection unit for storing paper dust, ink stains, and the like removed from the electrostatic attraction belt 2 by the cleaning blade 7.

A pressure roller 13 supported by the pressure plate 14 is disposed to face the conveyance roller 3. A tip pressure roller 15 is supported at the tip of the pressure plate 14. The tip pressurizing roller 15 functions to press the electrostatic attraction belt 2 against the platen 10 (see FIG. 3) disposed inside the upper side portion of the electrostatic attraction belt 2.
An entrance guide member 35 is disposed on the side of the transport roller 3 and guides the recording paper fed from the paper feed unit between the transport roller 3 (electrostatic adsorption belt 2) and the pressure plate 14. . The recording sheet electrostatically attracted to the upper surface of the electrostatic adsorption belt 2 is conveyed from the right to the left, that is, in the sub-scanning direction by the electrostatic adsorption belt 2 that rotates counterclockwise in FIG.

On the downstream side of the tension roller 4, a paper discharge roller pair including a paper discharge roller 17 and a spur 18 is provided. The tension roller 4 is provided with a separation claw 19, and the recording paper separated from the electrostatic attraction belt 2 by the separation claw 19 is sent downstream by a paper discharge roller pair consisting of a paper discharge roller 17 and a spur 18. It is done.
A code wheel 8 is attached to the shaft of the transport roller 3. A slit is formed in the code wheel 8 (not shown), and a transmission type encoder sensor 9 for detecting the slit is provided. The code wheel 8 and the sensor 9 constitute a rotary encoder. As the rotary encoder of this example, it is preferable to use 300 LPI or more and 4800 CR or more.

FIG. 5 shows a transmission mechanism of a belt conveyance mechanism that is also used in the recording paper conveyance device described above. The driving force generated by the motor 201 is transferred to the conveying roller 3 via a speed reduction mechanism including a motor pulley 202, a timing belt 204, and a pulley (toothed pulley or timing pulley) 203 attached to one end face of the shaft of the conveying roller 3. Is transmitted to. The code wheel 8 is conventionally attached coaxially with the pulley 203 due to layout and cost problems. In this configuration, the code wheel 8 is opposite to one end face of the shaft of the conveying roller 3 to which the pulley 203 is attached. It is attached to one end face of.
This state is shown in FIG. 3-1, and the arrangement relationship of the pulley 203, the conveying roller 3, and the code wheel 8 is as follows. "Place where the transmission mechanism part is attached to the movable part" It corresponds to the arrangement relationship in which the position detector is arranged at “a position away from”.

Here, it is assumed that the code wheel 8 and the encoder sensor 9 are attached to one end surface of the conveying roller 3 opposite to the pulley 203, but position data for detecting the twist between the pulley 203 and the conveying roller 3 is assumed. Therefore, if the encoder is not arranged on the motor, the timing belt, or the pulley, the configuration in which the encoder pattern is created on the electrostatic attraction belt 2 if there is no problem in resolution, seam, etc. A configuration in which an encoder is arranged on the tension roller 4 can also be adopted.
Since the position of the conveyance roller 3 or the electrostatic adsorption belt 2 is directly detected by such an arrangement of the encoder, the twist between the pulley 203 and the conveyance roller 3 is not detected as an encoder value. The encoder value accurately indicates the displacement of the recording paper and the electrostatic attraction belt 2 that conveys the recording paper.

  FIG. 4 is an example of a linear stage used in a machine tool, a manufacturing apparatus, an inspection apparatus, or the like. The linear stage 110 includes a linear guide composed of rolling guides (roller bearings), a ball screw 111, a carriage 112 that is restrained by the linear guide and moves in one axial direction by the ball screw 111, a motor 113 that drives the ball screw 111, The linear encoder 114 detects the position of the carriage 112. Here, the motor drive circuit and the control circuit are omitted.

Next, the positioning characteristics of the micro area of the mechanism having a large load and low rigidity will be described by taking the recording paper conveyance device 1 of the inkjet engine 20 as an example. If the apparatus has a large load and rigidity is a problem, the linear stage or the like has the same characteristics.
In the following, it is assumed that the resonance frequency of the transmission mechanism system including the motor 201, the motor pulley 202, the timing belt 204, and the pulley 203 is sufficiently higher than the resonance frequency between the pulley 203 and the conveying roller 3, and is in the form of a rigid body. explain. In practice, this resonance frequency must also be considered.

  In the coarse movement region (when moving a large distance), the shaft of the transport roller 3 or the pulley 203 attached to the shaft of the transport roller 3 is slightly elastically deformed by the torque generated by the motor. This elastic deformation occurs due to the sum of the torque necessary for the electrostatic attraction belt 2 as a movable part to start moving and the torque necessary for acceleration. A response substantially equivalent to the response of the inertial system is exhibited with the elastic deformation amount being a predetermined deformation amount. This response is represented by a spring and mass model as shown in FIG. In the linear motion system, the torque, inertia, angle, angular velocity, and angular acceleration may be replaced with force, mass, position, velocity, and acceleration, respectively, in the rotation system. A region exhibiting such characteristics is referred to herein as an inertia region. Since the elastic deformation is a minute amount, the influence is small in the coarse movement region.

  In the fine movement region (when moving a small distance), in addition to the elastic deformation of the shaft of the transport roller 3 or the pulley attached to the shaft of the transport roller 3, the characteristics of the contact portion between the surface of the transport roller and the electrostatic adsorption belt 2 The influence of the characteristics of the bearing portion of the transport roller shaft is increased. In the fine movement region, the viscoelastic characteristics of the contact portion and the bearing portion are affected. It has been confirmed that there are two types of characteristics in the fine movement region.

  The first is an area in which the pulley 203 moves by several μm to several tens of μm in terms of movement distance due to elastic deformation (hereinafter referred to as “elastic area”). FIG. 7 shows the torque-displacement response. When the motor torque is increased, the pulley 203 at one end of the transport roller moves corresponding to several μm to several tens of μm in terms of the moving distance. On the contrary, when the torque is decreased, the pulley 203 is elastically restored to almost zero. Return. Although there is some hysteresis, the pulley 203 shows a motion proportional to the motor torque. In addition, the electrostatic adsorption belt hung on the conveyance roller does not exhibit the same displacement as the pulley 203 because the conveyance roller and the pulley have elastic deformation and the viscoelastic characteristics, but the number of displacements of the pulley 203 is not. It is displaced by a range from a fraction of 1 to a few tens of 1 and shows a characteristic proportional to the motor torque (characteristic of “electrostatic attracting belt surface” in FIG. 7). In other words, the displacement of the pulley 203 and the displacement of the electrostatic attraction belt surface have a proportional relationship.

  The second is an area in which the pulley 203 moves by several tens of μm to several hundreds of μm in terms of movement distance, and this area has a large hysteresis (hereinafter referred to as “transition area”). The torque-displacement response in this region is shown in FIG. When the motor torque is increased, the pulley 203 of the transport roller 3 moves corresponding to several tens of μm to several hundreds of μm in terms of the moving distance, and unlike the movement in the inertial region, displacement occurs according to the motor torque. On the contrary, when the motor torque is reduced, the pulley 203 does not return to 0 even when the motor torque becomes 0, and exhibits a hysteresis characteristic as shown in FIG. In addition, the electrostatic attraction belt 2 wound around the transport roller 3 exhibits a smaller displacement than the pulley 203 due to elastic deformation of the transport roller 3 and the pulley 203 and the viscoelastic characteristics in the elastic region. It is the same. However, when the motor torque is set to 0, the same displacement as the pulley 203 is converged. These responses are represented by a spring and mass model as shown in FIG. The difference from FIG. 6A is that a spring k2 is added to the movable part. In the elastic region, it is considered that the contribution of the elasticity (spring characteristics) of the bearing of the conveyance roller shaft and the contact portion between the conveyance roller surface and the electrostatic attraction belt is large.

  On the other hand, in the transition region, as the force Fmf increases, it moves beyond the elastic (spring characteristic) region of the bearing portion of the conveying roller shaft and the contact portion between the surface of the conveying roller 3 and the electrostatic attraction belt 2. I believe. In the figure, it means that the wall supporting the spring k2 moves according to the force. Since it moves beyond the elastic region of the spring k2, a hysteresis is generated in which the displacement does not return even if the torque is zero. The pulley 203 and the electrostatic adsorption belt surface finally coincide with each other because the force F is zero because the friction Fsμ1 of the transmission mechanism portion is sufficiently small, and the transmission mechanism portion is in a position where the spring k1 is opened and the movable portion is stopped. Is considered to be imitated.

Therefore, regarding the controller for the coarse movement region (first controller), when the deformation of the spring k1 in FIG. 6A is considered to be minute, the influence of this is small (can be ignored) A controller that takes into account the inertia or weight of the transmission mechanism and the movable part.
The controller for the fine movement region (second controller) is a controller that takes into account the inertia or weight of the transmission mechanism portion and the movable portion, and the springs k1 and k2. Thus, the order of the fine movement controller is higher than that of the coarse movement controller. In this configuration, the displacement xc of the movable part is fed back.
Further, in the fine movement region, there are nonlinear characteristics such as an elastic region and a transition region, and an integral characteristic is added to compensate for this.

Next, a general positioning control system will be described.
9 and 10 are block diagrams of a general positioning control system. FIG. 9 shows a positioning control system consisting of only a position feedback loop, and FIG. 10 shows a positioning control system consisting of a position and speed feedback loop.
The block diagram of FIG. 9 will be described. The control target value (target position) and the fed back position information are compared by the comparator 116, and the output is input to the position compensator 117 as a position deviation. The position compensator 117 performs multiplication of a predetermined gain and predetermined filtering, and outputs it as a voltage command value or a current command value and inputs it to the driver 118. The position compensator 117 is typified by classical control theory such as PID, phase advance and phase lag, and state feedback based on modern control theory that feeds back the state quantity of the control target 121 and H∞ control (not shown). Any compensation method such as robust control theory may be used.

The driver 118 is composed of a voltage control driver for supplying a motor voltage corresponding to the voltage command value or a current control driver for supplying a motor current corresponding to the current command value. Here, a description will be given assuming that a current control driver having a simple transfer characteristic is used. The servo motor 119 is driven by a driver (current control driver) 118 with a motor current corresponding to a command current from the position compensator 117. The driving force of the motor drives the controlled object 121 via the transmission mechanism. The rotational position or position of the control object is detected by the position detector 120. The position detector 120 includes the linear encoder 114 in FIG. 4 and the code wheel 8 and the encoder sensor 9 in FIG. The position information detected by the position detector 120 is fed back to the comparator 116.
The servo motor 119 is a motor with a DC brush, a DC brushless motor, an AC servo motor, or the like. Depending on the type of the servo motor 119, the driving form of the driver 118 (single phase, three phase, Hall element input, etc.) also changes.

  The block diagram of FIG. 10 will be described. The control target value (target position) and the fed back position information are compared by the comparator 128, and the output is input to the position compensator 129 as a position deviation. The position compensator 129 performs multiplication of a predetermined gain and predetermined filter processing, and outputs a target speed. The output target speed and the speed information fed back are compared by the comparator 130, and the output is input to the speed compensator 131 as a speed deviation. From the speed compensator 131, a predetermined gain multiplication or a predetermined filter process is performed and output as a voltage command value or a current command value and input to a driver (current control driver) 118. The position compensator 129 and the speed compensator 131 are, for example, a state control based on a classical control theory such as PID, phase advance or phase lag, or a modern control theory that feeds back a state quantity of the controlled object 121, but not shown. Any compensation method such as robust control theory represented by ∞ control may be used.

  The driver 118 may be either a voltage control driver for supplying a motor voltage corresponding to the voltage command value or a current control driver for supplying a motor current corresponding to the current command value. In this embodiment, a current control driver having a simple transfer characteristic is used. The servo motor 119 is driven by a motor (corresponding to a command current from the speed compensator 131) by a driver (current control driver) 118. The driving force of the motor drives the control object 121 by the transmission mechanism. The rotation position or position of the control object 121 is detected by the encoder (position detector) 132. The encoder 132 is based on the linear encoder 114 in FIG. 4, the code wheel 8 and the encoder sensor 9 in FIG. Position information detected by the encoder 132 is fed back to the comparator 128.

  The position information detected by the encoder 132 is input to the speed calculation unit 134, converted into speed information, and fed back to the comparator 130. In the speed calculation unit, speed information can be obtained by a difference in position information for each predetermined period or a method (F / V conversion or the like) for measuring a period of position information.

The servo motor 119 is a motor with a DC brush, a DC brushless motor, an AC servo motor, or the like. Depending on the type of the servo motor 119, the driving form of the driver 118 (single phase, three phase, Hall element input, etc.) also changes.
A positioning control device capable of stable and highly accurate positioning is realized by combining the general positioning control system with a configuration and a method for operating the characteristics described in the coarse motion region and the fine motion region. A configuration for this will be described.

  In the case of the positioning control system including only the position feedback loop of FIG. 9, the internal configuration of the position compensator 117 is as shown in FIG. Inside the position compensator, there are a fine motion compensator 160, a coarse motion compensator 161, and a switcher 162. In the coarse motion compensator 161, a position compensator corresponding to the model shown in FIG. 6A is designed and mounted. The model may be designed as an inertia system that ignores the spring k1 between the transmission mechanism and the movable part, and considers the mass or inertia of the transmission mechanism and the movable part as one.

The fine motion compensator 160 is designed and mounted with a position compensator corresponding to a model made up of the mass or inertia of each of the transmission mechanism and the movable part and the springs k1 and k2 shown in FIG.
In the case of the positioning control system comprising the position and speed feedback loop of FIG. 10, the internal structure of the speed compensator 131 is as shown in FIG. Inside the speed compensator, there are a fine motion compensator 163, a coarse motion compensator 164, and a switch 165 thereof. The coarse motion compensator 164 is a speed compensator corresponding to the model as shown in FIG. The model may be an inertia system that ignores the spring k1 of the transmission mechanism and the movable part, and considers the mass or inertia of the transmission mechanism and the movable part as one.

The fine motion compensator 163 is a speed compensator corresponding to a model including the masses or inertias of the transmission mechanism unit and the movable unit shown in FIG. 6B and springs k1 and k2.
The inside of the position compensator 129 is represented in FIG. 11 similarly to the position compensator 117 of FIG. The coarse motion compensator 161 and the fine motion compensator 160 at this time are designed in accordance with the characteristics when the coarse motion compensator 164 or the fine motion compensator 163 of the speed feedback loop is used. Generally, since it is considered that disturbance can be suppressed by the speed feedback loop, a simple proportional gain (P) is often used. Further, depending on conditions, the coarse motion compensator 161 may perform a calculation to generate a speed profile up to a predetermined position deviation. In this case, when it falls within a predetermined position deviation, the fine movement compensator 160 is switched.

  The position compensator 117 of FIG. 9 and the fine motion compensator 160 and the coarse motion compensator 161 of the position compensator 129 of FIG. 10 described above are classical controls such as PID (proportional, integral, differential), phase advance and phase lag. It may be based on any theory such as a theory, a state feedback based on a modern control theory that feeds back a state quantity (not shown), or a robust control theory represented by H∞ control.

A form when mounted on an actual machine will be described. The position compensator, speed compensator, and position correction unit of the positioning control device can be configured by an analog circuit, a dedicated circuit such as an ASIC, or an arithmetic unit such as a CPU or DSP. Here, an example in which a DSP is used exclusively for the positioning control device will be described with reference to FIG.
The DSP 139 dedicated to the control operation and the host CPU 137 exchange information on target values and data such as drive modes via the host interface 138. The host interface 138 is a serial interface, a parallel interface, a shared memory, a predetermined register, or the like. The DSP 139 performs control calculation based on the calculation program stored in the ROM 140. Data at the time of calculation is stored in the RAM 141. In order to speed up the control calculation, a program in the ROM 140 may be loaded into the RAM 141 at the time of initialization and executed on the RAM.

Assuming that the encoder is an incremental rotary encoder 143, and the A-phase and B-phase pulses are output from the encoder, the counter 142 counts the pulses from the encoder. Generally, a value obtained by multiplying the A-phase B-phase pulse by 4 is counted, and the up / down is determined from the phase difference between the A-phase and the B-phase. The DSP 139 reads the position information from the counter 142 and sets a value corresponding to the command current value in the DAC 145 based on the result of a predetermined control calculation. The DAC 145 supplies a voltage corresponding to the current value to the motor driver 146, and the motor driver 146 drives the motor. Here, the motor driver 146 is a current control driver, and the current control is performed inside the driver. However, a configuration in which the detected motor drive current is fed back to the DSP via an ADC (not shown) and the current control is performed by the DSP. is there. There is also a motor driver configuration in which the voltage value can be set directly from the DSP 139 via the DSP bus. In general, the PWM method is the main driving method of the motor driver, but in the case of a precise stage, there is also a linear method.
When detecting the speed from the encoder pulse, there are a method of calculating a difference by the DSP 139, a method using an F / V conversion circuit (not shown), and a method such as a speed counter that measures a pulse interval by a basic clock (not shown). .

Next, the operation of the positioning control device of the present application will be described (see FIG. 14). Here, it is assumed that the DSP 139 processes each step required for positioning control and will be described based on the block diagrams of FIGS.
Here, the first control step will be described as the coarse motion control step (S3), and the second control step will be described as the fine motion control step (S4). In addition, the target position described here is the forward direction. Therefore, in the case of the target position in the negative direction, the sign of the position deviation and the determination of its magnitude change. The absolute value of the position deviation may be used to determine the position deviation due to the sign problem.
The control DSP 139 dedicated to control receives information on the target position xref from the host CPU 137 via the host interface 138. If the position deviation ex between the target position and the current position is equal to or greater than the predetermined value ex1 (S2), the DSP 139 performs a coarse motion control step (S3). In the coarse motion control step (S3), the DSP 139 switches the position compensator and the velocity compensator to the respective coarse motion compensators.

  In the block diagram, it is expressed as a switch 162 or switch 165. However, when processing is performed by the DSP 139, it is switched by software such as change of calculation parameter or change of function to be called. The comparator 128 compares the corrected target position xref with the position information fed back from the encoder 132 and outputs a position deviation ex. The position deviation ex is input to a coarse motion compensator 161 of a position compensator to perform position compensation calculation. The calculation result is compared with the speed information output and fed back as the target speed by the comparator 130, and the speed deviation ev is output. The speed deviation ev is input to the coarse compensator 164 of the speed compensator, and the speed compensation is calculated. The calculation result is passed to the motor driver 118 as a target current value via a DAC or the like, and the motor driver 118 drives the servo motor 119 by passing a current corresponding to the target current value. Torque or force generated by the servo motor drives the movable part via the transmission mechanism part.

An encoder 120 is attached to the movable part, and position information of the encoder 120 and speed information calculated from the position information are fed back. The mechanism model in the coarse motion control step is shown in FIG. 9 and 10, the transmission mechanism unit and the movable unit are collectively shown as the control object 121.
When the position deviation becomes smaller than the predetermined position deviation ex1 in the movement by the coarse movement control step (S2), the calculator DSP139 dedicated to the control calculation performs the fine movement control step (S4), and the position compensator and the speed compensator The inside is switched to each fine motion compensator. In the block diagram, it is expressed as a switch 162 or switch 165. However, when processing is performed by the DSP 139, it is switched by software such as change of calculation parameter or change of function to be called.

  The comparator 128 compares the corrected target position xref with the position information fed back from the encoder 132 and outputs a position deviation ex. The position deviation is input to the fine compensation compensator 160 of the position compensator and the position compensation is calculated. The calculation result is compared with the speed information output as the target speed and fed back by the comparator 130, and the speed deviation ev is output. The speed deviation ev is input to the fine motion compensator 163 of the speed compensator to perform speed compensation calculation. The calculation result is passed to the motor driver 118 as a target current value via a DAC or the like, and the motor driver 118 drives the servo motor 119 by passing a current corresponding to the target current value. The torque or force generated by the servo motor 119 drives the movable part via the transmission mechanism part. An encoder is attached to the movable part, and position information of the encoder 132 and speed information calculated from the position information are fed back. The mechanism model in the fine movement control step is shown in FIG. 9 and 10, the transmission mechanism unit and the movable unit are collectively shown as the control object 121.

In the above description, the description of feedforward that has the effect of improving the proportional gain for signal conversion from pulse to position, current value to voltage value, etc. and the followability to the target value is omitted, but it is implemented in the actual machine be able to.
Further, the positioning control system having the position and speed feedback loop of FIG. 10 has been described in both the coarse motion control step and the fine motion control step. However, the positioning control system may use the positioning control system of only the position feedback of FIG. good. Further, in the coarse motion control step (S3), the positioning control system having the position and speed feedback loop of FIG. 10 is used, and in the fine motion control step (S4), the positioning control system of only the position feedback of FIG. 9 is used. May be. In particular, in the fine movement control step (S4), the speed information becomes coarse due to the resolution of the encoder. Therefore, it is an effective means to use a positioning control system with only position control feedback. Even when the tachometer is used instead of the encoder information for the speed detection method, the above method is an effective means because the S / N deteriorates in the low speed region.

  In the above description of the operation, it has been described that the DSP 139 dedicated to control computation performs the switching between the coarse motion controller and the fine motion controller, and the coarse motion control step and the fine motion control step. However, the host CPU 137 and the DSP 139 are connected via the host interface 138. By performing handshaking of the target position, encoder information, operation flag, etc., the host CPU 137 can always manage the current position x and switch to the corresponding step. Step switching is performed by software in the host CPU 137, and an operation command is transmitted to the DSP 139 by an operation flag or the like via the host interface based on the result. Upon receiving this operation command, the DSP 139 can switch the position compensator and the speed compensator as shown in FIG. 11 and FIG. 12 configured in the DSP 139, so that the DSP 139 specializes in control calculation. be able to. Further, here, an example in which the control calculation is performed by the DSP 139 has been described. However, in order to increase the speed of the control calculation or to reduce the cost of the calculation circuit, the calculation unit may be an analog circuit, and the host CPU 137 may manage the steps. . In this case, the circuit can be switched by an analog switch or the like according to a command from the host CPU 137.

In the above description, the switching between the coarse motion control step (S3) and the fine motion control step (S4) is determined based on the magnitude of the position deviation ex with respect to the predetermined value ex1 (S5). Switching may not be successful and may cause instability and vibration. Therefore, the switching reference value is provided with hysteresis, and for this purpose, the switching reference from the coarse motion control step to the fine motion control step is the position deviation ex1, and the switching reference from the fine motion control step to the coarse motion control step is the position deviation ex2. The reference position deviation ex1 is set to a value smaller than the position deviation ex2.
| Ex1 | <| ex2 | (1)
As a result, the switching from the coarse motion control step to the fine motion control step is smooth, and there is no switching from the fine motion control step to the coarse motion control step due to some vibration or the like.
The switching operation between the coarse motion control step and the fine motion control step when hysteresis is given to the switching reference is also performed according to the flow shown in FIG. 14 (flow diagram).

As shown in FIGS. 1 to 3 and 5, when the above-described positioning control device of the present application is applied to the sub-scanning recording paper transport mechanism of the image forming apparatus of the ink jet recording system, the control is performed as shown in FIGS. The system is configured as shown in FIGS.
The positioning control device is configured as shown in FIG. 13, and the switching operation is performed according to the flow shown in FIG.

As described above, the configuration and operation of the embodiment have been described by taking the image forming apparatus and the linear stage as examples. However, a mechanism that transmits power (not linear motion) via the transmission mechanism and has a large load on the object and low rigidity is provided. The present invention can be applied as long as positioning is performed with high accuracy.
For example, a case where the object on the belt is positioned with high accuracy by the belt conveyance mechanism is conceivable.

These are cross-sectional block diagrams which show an example of the inkjet recording device provided with the paper conveying apparatus based on this invention. FIG. 2 is a detailed view showing in detail the configuration of a recording paper transport apparatus 1 in the ink jet recording apparatus of FIG. 1. FIG. 2 is an enlarged side view of a printing unit in the ink jet recording apparatus of FIG. 1. FIG. 3 is a front view illustrating a positional relationship between a pulley, a conveyance roller, and a position detector (encoder) of the recording paper conveyance device. These are side views of an example of a linear stage used in a machine tool, a manufacturing apparatus, an inspection apparatus, or the like. These are side views of a transmission mechanism of a belt conveyance mechanism that is also used in a recording paper conveyance device. (A) is a schematic diagram showing the response of the inertial system due to the motor driving torque as a spring and mass model, and (b) is the response of the inertial system with the spring k2 added to the movable part as a model of the spring and mass. It is a schematic diagram. These are the correlation diagrams which show the response of the torque-displacement about the displacement of the pulley electrostatic attraction belt surface in the area | region (elastic area | region) to which the pulley 203 moves equivalent to several micrometers-several tens of micrometers in conversion of movement distance. These are correlation diagrams showing the torque-displacement response for the displacement of the pulley and the surface of the electrostatic attraction belt in a region where the pulley 203 moves equivalent to several tens of μm to several hundreds of μm in terms of moving distance (transition region where hysteresis is large). . FIG. 3 is a block diagram of a general positioning control system, and is a block diagram of a positioning control system including only a position feedback loop. FIG. 3 is a block diagram of a general positioning control system, which is a block diagram of a positioning control system including a position and speed feedback loop. 9 is a block line showing an example of the internal configuration of the position compensators 117 and 119 in the case of the positioning control system consisting only of the position feedback loop of FIG. 9 and the positioning control system consisting of the position and velocity feedback loop of FIG. FIG. FIG. 11 is a block diagram showing an example of an internal configuration of a speed compensator 131 in the case of a positioning control system including the position and speed feedback loop of FIG. 10. These are explanatory drawings of the example which uses DSP exclusively for a positioning control apparatus. These are the flowcharts of the example which uses DSP exclusively for a positioning control apparatus.

Explanation of symbols

1: recording paper transport device 2: electrostatic adsorption belt 3: transport roller 4: tension roller 8: code wheel 9: encoder sensor 10: platen 17: paper discharge roller 18: spur 22: print head 111: ball screw 112: carriage 113, 201: Motor 114: Linear encoder 116, 128, 130: Comparator 117, 129: Position compensator 118: Driver 119: Servo motor 120, 132: Position detector (encoder)
121: Control target 131: Speed compensator 160, 163: Fine motion compensator 161, 164: Coarse motion compensator 162, 165: Switch 203: Pulley 204: Timing belt

Claims (11)

A single motor, a transmission mechanism that transmits the driving force of the motor, a movable portion that is driven by transmission of the driving force of the motor, a positioning mechanism that includes a position detector, and an output of the position detector are fed back. A low-rigidity structure including a control calculation unit that performs a predetermined calculation and a control mechanism that includes a driver unit that drives the motor based on the output of the control calculation unit, and the transmission mechanism unit or the movable unit exhibits torsional characteristics. In a positioning control device that is configured from a member and performs positioning control at a target position,
A positioning control device comprising: the position calculation unit disposed at a position away from a place where the transmission mechanism unit is attached to the movable unit, and the control calculation unit considering the torsion characteristics. . The positioning control device according to claim 1,
A control controller including a first controller that takes into account characteristics when the movable part largely moves; and a second controller that takes into account characteristics of a minute region;
A first control step for setting a target position and performing positioning by the first controller; and a second control step for performing positioning by the second controller when a predetermined positional deviation is reached with respect to the target position. A positioning control device characterized by that.   The positioning control device according to claim 2, wherein the second controller is configured in consideration of the fact that the order of the control target is larger than that of the first controller.   The positioning control device according to claim 2, wherein hysteresis is given to a predetermined position deviation for switching between the first control step and the second control step.   3. The positioning control apparatus according to claim 2, wherein the first control step and the second control step are switched by a computing unit at a higher level.   3. The positioning control device according to claim 2, wherein the first control step and the second control step are switched by a calculator that constitutes the control calculation unit.   An image forming apparatus comprising the positioning control device according to claim 1. The control target value and the fed back position information are compared by the comparator, and the output is input as a position deviation to the position compensator.
3. The positioning control device according to claim 2, wherein the position compensator performs multiplication of a predetermined gain and predetermined filtering, and outputs the voltage command value or the current command value to the driver.   9. The positioning control device according to claim 8, wherein the position compensator is constituted by a fine motion compensator, a coarse motion compensator, and a switch between them. The control target value and the fed back position information are compared by the comparator, and the output is input as a position deviation to the position compensator.
The position compensator performs a predetermined gain multiplication or a predetermined filter process to output a target speed,
The output target speed and the speed information to be fed back are compared by a comparator, and the output is input as a speed deviation to the speed compensator.
3. The positioning control device according to claim 2, wherein a voltage command value or a current command value is output from the speed compensator by a predetermined gain multiplication or a predetermined filter process and input to the driver.   11. The positioning control device according to claim 10, wherein the position compensator and the speed compensator are constituted by a fine motion compensator, a coarse motion compensator, and a switch between them.

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