Carriage speed correction method and printer

Abstract

The rotational speed of a motor 44 of a printer 10 is controlled on the basis of the rotational position of a motor shaft 44a, which is measured by a motor encoder 44b. The present method includes: a step S03 for rotating the motor so that the rotational speed based on the measurement from the motor encoder 44b is constant, and causing a carriage 30 to travel; a step S04 for measuring the position of the carriage 30 in the traveling direction by means of a linear encoder 45; a step S06 for calculating the difference between the rotational position of the motor shaft 44a based on the measurement from the motor encoder 44b and the rotational position of the motor shaft 44a based on the measurement from the linear encoder 45 at a plurality of rotational positions over one turn of the motor shaft 44a or a plurality of turns of the motor shaft 44a; and a step S07 for determining, on the basis of the calculated difference, a correction value to be added to the rotational position of the motor shaft 44a measured by the motor encoder 44b so that the change in the rotational speed during one turn of the motor shaft 44a based on the measurement from the linear encoder 45 decreases.

Description

Technical Field

[0001] The present invention relates to a method for correcting the speed of a carriage of a printer and a printer.

Background Art

[0002] A printer that prints an image on a recording medium while causing a carriage equipped with a print head to travel in a predetermined scanning direction has been conventionally known. For example, Patent Document 1 discloses an inkjet printer that includes an electric motor that causes an inkjet head to travel and a linear scale, and obtains travel position data of the inkjet head by reading the position of the inkjet head in the scanning direction from the scale engraved on the linear scale. The inkjet printer disclosed in Patent Document 1 is configured to correct the measured travel distance read from the linear scale with the actual travel distance of the inkjet head calculated from the rotation angle of the electric motor in consideration of the expansion and contraction of the linear scale due to weather conditions.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Many motors with controllable rotational speed are equipped with a motor shaft and a motor encoder that measures the rotational position of the motor shaft, and are configured to control the rotational speed based on the rotational position of the motor shaft measured by the motor encoder. As shown in Patent Document 1, the rotational position of the motor shaft measured by the motor encoder is considered to be correct. However, the inventors of this invention have noticed that in such motors, even when controlled to rotate at a constant speed, the speed may change within one rotation of the motor shaft. According to the inventors of this invention, this is due, for example, to eccentricity between the motor shaft and the motor encoder. When there is eccentricity between the motor shaft and the motor encoder, the motor encoder cannot correctly measure the rotational position of the motor shaft, and the rotational speed of the motor is controlled based on an incorrect rotational position of the motor shaft. As a result, even when controlled to rotate at a constant speed, the speed changes within one rotation of the motor shaft. If a motor has such a characteristic of speed change, the speed of the carriage changes within one rotation of the motor shaft.

[0005] The present invention has been made in view of the above, and its object is to provide a method for reducing changes in carriage speed caused by changes in the rotational speed of the motor that drives the carriage within one rotation in a printer. [Means for solving the problem]

[0006] The method disclosed herein is a method for correcting the speed of a carriage in a printer comprising a print head, a carriage on which the print head is mounted and which travels in a predetermined scanning direction, and a motor that travels the carriage. The motor comprises a motor shaft and a motor encoder for measuring the rotational position of the motor shaft, and the rotational speed of the motor is controlled based on the rotational position of the motor shaft measured by the motor encoder. The method disclosed herein includes a preparation step, a travel step, a measurement step, a first calculation step, a second calculation step, a determination step, and a correction step. In the preparation step, a linear encoder capable of measuring the position of the carriage in the scanning direction is prepared. In the travel step, the motor is rotated so that the rotational speed based on the measurement of the motor encoder is constant, and the carriage is traveled. In the measurement step, the position of the carriage in the scanning direction during the travel step is measured by the linear encoder. In the first calculation step, the rotational position of the motor shaft during the travel step is determined based on the measurement of the linear encoder. In the second calculation step, the difference between the rotational position of the motor shaft based on the measurement of the motor encoder and the rotational position of the motor shaft based on the measurement of the linear encoder is determined at multiple rotational positions over one or more rotations of the motor shaft. In the determination step, based on the difference calculated in the second calculation step, a correction value is determined to be added to the rotational position of the motor shaft measured by the motor encoder so as to reduce the change in the rotational speed of the motor shaft within one rotation based on the measurement of the linear encoder. In the correction step, the correction value is added to the rotational position of the motor shaft measured by the motor encoder.

[0007] Furthermore, the printer disclosed herein includes a print head, a carriage on which the print head is mounted and which travels in a predetermined scanning direction, a motor that drives the carriage, a linear encoder capable of measuring the position of the carriage in the scanning direction, and a control device. The motor includes a motor shaft and a motor encoder that measures the rotational position of the motor shaft, and the rotational speed of the motor is controlled based on the rotational position of the motor shaft measured by the motor encoder. The control device includes a travel control unit, a measurement control unit, a first calculation unit, a second calculation unit, a correction value determination unit, and a correction unit. The travel control unit rotates the motor so that the rotational speed based on the measurement of the motor encoder is constant, and drives the carriage. The measurement control unit measures the position of the carriage in the scanning direction with the linear encoder when the carriage is traveling under the control of the travel control unit. The first calculation unit determines the rotational position of the motor shaft while the carriage is traveling based on the measurement of the linear encoder. The second calculation unit determines the difference between the rotational position of the motor shaft based on the measurement of the motor encoder and the rotational position of the motor shaft determined by the first calculation unit, at multiple rotational positions over one or more rotations of the motor shaft. Based on the difference calculated by the second calculation unit, the correction value determination unit determines a correction value to be added to the rotational position of the motor shaft measured by the motor encoder, so as to reduce the change in the rotational speed of the motor shaft based on the measurement of the linear encoder within one rotation. The correction unit adds the correction value to the rotational position of the motor shaft measured by the motor encoder.

[0008] According to the above method, by actually moving the carriage in the travel step and measurement step and having the motor encoder and linear encoder take measurements, a correction value can be obtained that is added to the rotational position of the motor shaft measured by the motor encoder, and that reduces the change in the rotational speed of the motor shaft within one rotation based on the measurement by the linear encoder. The rotational speed of the motor shaft based on the measurement by the linear encoder represents the actual rotational speed of the motor shaft. Therefore, according to the above method, it is possible to reduce the change in the carriage speed caused by the change in the rotational speed of the motor that moves the carriage within one rotation. The above printer can also achieve a similar effect. [Brief explanation of the drawing]

[0009] [Figure 1] This is a front view of a printer according to one embodiment. [Figure 2A] This is a schematic diagram showing the configuration of a carriage motor. [Figure 2B] This diagram schematically shows the part related to the rotation control of the carriage motor. [Figure 3] This graph shows the deviation in motor shaft position detection due to eccentricity. [Figure 4] This is a flowchart showing the procedure for correcting the rotational speed of the carriage motor. [Figure 5] This block diagram shows the rotational control of a carriage motor, including eccentricity correction processing. [Figure 6] This is a block diagram showing the processing procedure for eccentricity correction. [Figure 7] This graph compares the carriage speed before and after correction. [Figure 8] This flowchart shows the details of the second calculation step. [Figure 9] This graph shows the eccentricity of the carriage motor. [Figure 10] This graph shows the eccentricity after noise removal. [Figure 11]This graph shows the phase difference and gain in the graph indicating the eccentricity after noise removal. [Figure 12] This is a graph of eccentricity illustrating another method for determining the phase difference. [Figure 13] This graph of eccentricity shows yet another method for determining the phase difference. [Figure 14] This is a block diagram of a printer according to another embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, an inkjet printer (hereinafter simply referred to as "printer") according to an embodiment of the present invention will be described with reference to the drawings. Naturally, the embodiments described herein are not intended to particularly limit the present invention. Furthermore, the same reference numerals are used for components and parts that perform the same function, and redundant explanations are omitted or simplified as appropriate.

[0011] [Printer configuration] Figure 1 is a front view of the printer 10 according to this embodiment. In the following description, left, right, up, and down refer to the left, right, up, and down directions as seen from the perspective of an operator standing in front of the printer 10. Also, when the operator is facing the front of the printer 10, the direction from the rear of the printer 10 toward the operator is defined as the front, and the direction from the operator toward the rear of the printer 10 is defined as the rear. The symbols L, R, U, and D in the drawing represent left, right, up, and down, respectively.

[0012] The printer 10 prints on the recording medium 5 while moving it in the sub-scanning direction. In this case, the sub-scanning direction is the front-to-back direction. The printer 10 also ejects ink from the print head 20 while moving it in the main scanning direction Y, which is perpendicular to the sub-scanning direction. In this case, the main scanning direction Y is the left-to-right direction. Here, the main scanning direction Y, the sub-scanning direction, and the up-and-down direction are perpendicular to each other. However, the above directions are for illustrative purposes only and do not limit the installation configuration of the printer 10 in any way.

[0013] The recording medium 5 is, for example, recording paper. However, the recording medium 5 is not limited to recording paper. The recording medium 5 includes, in addition to papers such as plain paper and inkjet printing paper, those formed from resin materials such as polyvinyl chloride (PVC) and polyester, metal plates formed from aluminum, iron, etc., glass plates, wood plates, and those formed from cardboard, etc.

[0014] As shown in FIG. 1, the printer 10 includes a platen 15, a print head 20, a carriage 30 that mounts the print head 20 and travels in the main scanning direction Y, a carriage moving device 40 that causes the carriage 30 to travel in the main scanning direction Y, and a conveyance device 50 that conveys the recording medium 5 in the sub-scanning direction, and a control device 60.

[0015] The platen 15 is a support base that supports the recording medium 5. The platen 15 extends in the main scanning direction Y and the sub-scanning direction. The carriage 30 is provided above the platen 15. The print head 20 is provided on the carriage 30. The print head 20 includes a plurality of ink heads 21. The plurality of ink heads 21 each extend in the sub-scanning direction. The plurality of ink heads 21 are arranged side by side in the main scanning direction Y. The plurality of ink heads 21 may be arranged so that their positions in the sub-scanning direction are aligned, or may be arranged in a so-called staggered arrangement such that the positions of some or all of them in the sub-scanning direction are shifted. The number and arrangement of the ink heads 21 are not particularly limited.

[0016] Each ink head 21 has a plurality of nozzles (not shown) from which ink is ejected. The plurality of nozzles are arranged in a line in the sub-scanning direction. The ink is ejected downward from the nozzles and lands on the recording medium 5 on the platen 15. Each ink head 21 is equipped with, for example, a plurality of piezoelectric elements. Each ink head 21 ejects ink when the piezoelectric elements vibrate in response to a drive signal transmitted from the control device 60. However, the actuators provided by the ink head 21 are not limited to piezoelectric elements. The ink head 21 may be, for example, a continuous inkjet head of various types such as a binary deflection type or a continuous deflection type, or an on-demand inkjet head such as a thermal type.

[0017] The ink ejected from the print head 20 is not particularly limited. The ink ejected from the print head 20 may be, for example, a solvent-based pigment ink, a water-based ink, a photocurable ink (for example, a UV-curable pigment ink that hardens when exposed to ultraviolet light, so-called UV ink), etc.

[0018] The carriage moving device 40 moves the carriage 30 in the main scanning direction Y. As shown in Figure 1, the carriage moving device 40 has a guide rail 41, left and right pulleys 42, an endless belt 43, and a carriage motor 44. The guide rail 41 is located above the platen 15. The guide rail 41 extends in the main scanning direction Y. The carriage 30 is configured to move along the guide rail 41 in the main scanning direction Y. The carriage 30 is fixed to the belt 43. The belt 43 is wrapped around the left and right pulleys 42. The carriage motor 44 drives the carriage 30 and is connected to one of the pulleys 42. When the carriage motor 44 is driven, one of the pulleys 42 rotates, causing the belt 43 to move. This moves the carriage 30 in the main scanning direction Y. The print head 20 moves with the carriage 30 in the main scanning direction Y.

[0019] Figure 2A is a schematic diagram showing the configuration of the carriage motor 44. Figure 2B is a schematic diagram showing the part related to rotation control of the carriage motor 44. As shown in Figures 2A and 2B, the carriage motor 44 comprises a motor shaft 44a and a motor encoder 44b that measures the rotational position of the motor shaft 44a. The carriage motor 44 is a motor whose rotational speed is controlled based on the rotational position of the motor shaft 44a measured by the motor encoder 44b. The motor shaft 44a is connected directly or indirectly to one of the pulleys 42. The motor encoder 44b comprises a disk 44c that rotates with the motor shaft 44a and a sensor 44d fixed to the motor casing (or stator). The disk 44c has a number of scales 44e formed along the circumferential direction, for example by printing. The sensor 44d is configured to detect the scales 44e on the disk 44c. The detection method of the scales of the sensor 44d may be optical, magnetic, or any other method. The motor encoder 44b measures the rotational position of the motor shaft 44a by detecting a scale 44e that rotates with the motor shaft 44a. Preferably, the motor encoder 44b is an absolute encoder that measures the absolute position from the rotation origin. However, if the rotation origin is detected by another method, it may be an incremental encoder that detects the relative position from any rotational position. In this case, the motor encoder 44b outputs a pulse signal each time the sensor 44d detects a scale 44e.

[0020] In this embodiment, the printer 10 is equipped with a linear encoder 45 capable of measuring the position of the carriage 30 in the main scanning direction Y. As shown in Figure 1, the linear encoder 45 comprises a scale 45a and a head 45b. The scale 45a has a number of scales (not shown) aligned in the main scanning direction Y. The scale 45a is fixed, for example, to a guide rail 41. The head 45b is fixed, for example, to the carriage 30. The head 45b is configured to detect the scales of the scale 45a. The method of detecting the scales of the head 45b may be optical, magnetic, or other. The linear encoder 45 measures the position of the carriage 30 in the main scanning direction Y by detecting the scales with the head 45b moving with the carriage 30. The position of the carriage 30 is measured based on the number of scales detected.

[0021] The transport device 50 moves the recording medium 5 in the sub-scanning direction. As shown in Figure 1, the transport device 50 includes a grid roller 51, a pinch roller 52, and a feed motor 53. The grid roller 51 is embedded in the platen 15. A portion of each grid roller 51 is exposed to the platen 15. The feed motor 53 rotates the grid roller 51 in the sub-scanning direction. The pinch roller 52 presses down on the recording medium 5 from above. The pinch roller 52 is positioned above the grid roller 51. The pinch roller 52 is positioned opposite the grid roller 51. The pinch roller 52 is configured to be movable in the vertical direction. When the feed motor 53 is driven and the grid roller 51 rotates with the recording medium 5 sandwiched between the grid roller 51 and the pinch roller 52, the recording medium 5 is transported in the sub-scanning direction.

[0022] The control device 60 is electrically connected to the multiple ink heads 21, the carriage motors 44 of the carriage moving device 40, and the feed motors 53 of the transport device 50, and controls their operation. The control device 60 is also electrically connected to the linear encoder 45 and receives signals from the linear encoder 45. The configuration of the control device 60 is not particularly limited. The control device 60 is, for example, a microcomputer. The hardware configuration of the microcomputer is not particularly limited, but for example, it includes an interface (I / F) for receiving print data etc. from external devices such as a host computer, a central processing unit (CPU) for executing instructions of the control program, a ROM (read-only memory) for storing the program executed by the CPU, a RAM (random access memory) used as a working area for expanding the program, and a storage device such as memory for storing the above program and various data. Note that the control device 60 does not necessarily have to be located inside the printer 10; for example, it may be a computer etc. installed outside the printer 10 and connected to the printer 10 via wired or wireless communication.

[0023] [Carriage velocity correction] The following describes a method for correcting the speed of the carriage 30. The method described below reduces the change in the speed of the carriage 30 by reducing the change in the rotational speed of the motor shaft 44a within one rotation. In the method according to this embodiment, a correction value is added to the rotational position of the motor shaft 44a, measured by the motor encoder 44b, so that the change in the rotational speed of the motor shaft 44a within one rotation is reduced.

[0024] [Velocity change due to eccentricity] First, let's explain why the rotational speed of the carriage motor 44 changes within one rotation. As schematically shown in Figure 2B, there may be a slight but significant eccentricity between the motor shaft 44a and the disk 44c. As shown in Figure 2B, when the disk 44c rotates with the motor shaft 44a while it is eccentric with respect to the motor shaft 44a, the scale 44e moves closer to or further away from the sensor 44d depending on the rotational position of the disk 44c. In the example in Figure 2, the scale 44e moves closer to or further away from the sensor 44d in the left-right direction shown in the figure. Therefore, when the motor shaft 44a and disk 44c rotate at a constant speed, the rotational speed of the motor shaft 44a measured by the motor encoder 44b will increase or decrease. The carriage motor 44 is configured to control its rotational speed based on the rotational position of the motor shaft 44a measured by the motor encoder 44b. Therefore, if the rotational speed of the motor shaft 44a is controlled to be constant based on the rotational position of the motor shaft 44a measured by the motor encoder 44b, the rotational speed of the motor shaft 44a actually changes within one rotation.

[0025] Figure 3 is a graph showing the deviation in the position detection of the motor shaft 44a due to eccentricity. The horizontal axis in Figure 3 represents the actual rotational position of the motor shaft 44a (unit: angle). The values ​​on the horizontal axis are based on the position of the carriage 30 measured by the linear encoder 45. The position of the carriage 30 measured by the linear encoder 45 reflects the actual rotational position of the motor shaft 44a. The vertical axis in Figure 3 represents the rotational position of the motor shaft 44a measured by the motor encoder 44b (unit: count of pulses output by the motor encoder 44b).

[0026] Graph G1 in Figure 3 is a graph showing the rotational position of the motor shaft 44a as measured by the motor encoder 44b, relative to the rotational position of the motor shaft 44a as measured by the linear encoder 45 (hereinafter also referred to as the actual rotational position of the motor shaft 44a), and shows the case when there is no eccentricity in the carriage motor 44. As shown in Figure 3, graph G1 is a straight line. Figure 2 is a graph representing the rotational position of the motor shaft 44a as measured by the motor encoder 44b relative to the actual rotational position of the motor shaft 44a, and shows the case where the carriage motor 44 is eccentric. As shown in Figure 3, graph G2 is a curve that intersects graph G1 at two points 180 degrees apart from each other, and is above graph G1 on one side of the intersection and below graph G1 on the other side of the intersection.

[0027] When the carriage motor 44, which exhibits these characteristics, is controlled to rotate at a constant speed, the speed of the carriage 30 follows a sine curve, as shown in graph G4 of Figure 7 (graph showing the speed before correction). The horizontal axis of Figure 7 represents the commanded position of the carriage 30. The vertical axis of Figure 7 represents the speed of the carriage 30 based on measurements by the linear encoder 45. One period of the sine curve corresponds to one rotation of the motor shaft 44a.

[0028] [Procedure for correcting the rotational speed of the carriage motor] Figure 4 is a flowchart showing the procedure for correcting the rotational speed of the carriage motor 44. As shown in Figure 4, the steps for correcting the rotational speed of the carriage motor 44 according to this embodiment include a motor encoder 44b counter initialization step S01, a linear encoder 45 preparation step S02, a travel step S03 for moving the carriage 30 at a constant speed, a measurement step S04 for measuring the position of the carriage 30 in the main scanning direction Y with the linear encoder 45, a first calculation step S05 for determining the rotational position of the motor shaft 44a, a second calculation step S06 for determining the difference between the rotational position of the motor shaft 44a based on the measurement by the motor encoder 44b and the actual rotational position of the motor shaft 44a, a determination step S07 for determining a correction value to be added to the rotational position of the motor shaft 44a measured by the motor encoder 44b, and a correction step S08 for adding the correction value to the rotational position of the motor shaft 44a measured by the motor encoder 44b.

[0029] In the motor encoder 44b counter initialization step S01, the counter value of the motor encoder 44b is set to zero. The counter value of the motor encoder 44b, which has been initialized to zero, serves as the reference point for phase offset measurement and correction in subsequent steps.

[0030] In preparation step S02, a linear encoder capable of measuring the position of the carriage 30 in the main scanning direction Y is prepared. Since the printer 10 according to this embodiment is equipped with a linear encoder 45, preparation step S02 is included in the process of manufacturing the printer 10. If the printer is not equipped with a linear encoder, a linear encoder may be temporarily attached to the printer.

[0031] In the travel step S03, the carriage motor 44 is rotated so that the rotational speed based on the measurement of the motor encoder 44b remains constant, and the carriage 30 is moved. In other words, the carriage motor 44 is controlled at a constant speed in a conventional manner. The rotational speed of the carriage motor 44 in the travel step S03 is set to be extremely slow. By setting the rotational speed of the carriage motor 44 to be extremely slow, the measurement resolution of the motor encoder 44b and the linear encoder 45 is increased, enabling high-precision correction. It is preferable that the rotational speed of the carriage motor 44 in the travel step S03 is at least slower than the rotational speed of the carriage motor 44 during printing. Preferably, the rotational speed of the carriage motor 44 in the travel step S03 is about 60 rpm. Preferably, the speed of the carriage 30 in the travel step S03 is about 20 mm / second.

[0032] In the measurement step S04, the position of the carriage 30 in the main scanning direction Y during the travel step S03 is measured by the linear encoder 45. This obtains data to determine the actual rotational position of the motor shaft 44a. In the first calculation step S05, the rotational position of the motor shaft 44a during the travel step S03 (actual rotational position) is determined based on the measurement by the linear encoder 45.

[0033] In the second calculation step S06, the difference between the rotational position of the motor shaft 44a based on the measurement of the motor encoder 44b and the rotational position of the motor shaft 44a based on the measurement of the linear encoder 45 is determined for multiple rotational positions over one or more rotations of the motor shaft 44a. G3 in Figure 3 is a graph of the difference obtained in the second calculation step S06 (however, for ease of viewing, the vertical axis scale is smaller than that of G1 and G2 and the graph is magnified vertically, with the center of the vertical axis as the zero point). As shown in Figure 3, graph G3 forms a sine curve. Note that in the example of Figure 3, the eccentricity error at the origin of the horizontal axis corresponds to zero on the sine curve, but this may shift depending on the angle of the motor shaft 44a during assembly.

[0034] In the determination step S07, based on the difference calculated in the second calculation step S06, a correction value is determined to be added to the rotational position of the motor shaft 44a measured by the motor encoder 44b, so as to reduce the change in the rotational speed of the motor shaft 44a (actual rotational speed) based on the measurement of the linear encoder 45 within one rotation. Here, the correction value includes a correction value for the amplitude (gain) of the sine curve and a correction value for the phase difference between the zero position and the origin of the sine curve. In the correction step S08, the correction value determined in step S07 is added to the rotational position of the motor shaft 44a measured by the motor encoder 44b. Specifically, for example, the correction value is stored in the control device 60, and the rotational position of the motor shaft 44a measured and fed back by the motor encoder 44b is corrected each time feedback is received. This reduces the change in the actual rotational speed of the carriage motor 44 within one rotation. That is, the speed of the carriage 30, which was getting faster and slower in a sine curve-like manner depending on the position of the carriage 30, is brought closer to a constant speed. Hereinafter, this process will also be referred to as eccentricity correction processing. In this embodiment, the calculation of the correction values ​​performed in steps S01 to S08 is performed during the manufacturing or maintenance of the printer 10, but it may also be performed during printing.

[0035] Figure 5 is a block diagram illustrating the rotational control of the carriage motor 44, including eccentricity correction processing. As shown in Figure 5, in the rotational control of the carriage motor 44 according to this embodiment, a command value for rotational speed is input to the control processing unit 61 of the control device 60, and feedback control is cyclically performed to achieve the rotational speed according to the command value. The output signal output by the control processing unit 61 is received by the motor driver 62. The motor driver 62 controls the rotation of the carriage motor 44 based on the received signal. For example, the motor driver 62 adjusts the current flowing to the carriage motor 44. The motor encoder 44b of the carriage motor 44 outputs a pulse signal each time it detects a scale 44e, for example. The pulse signal is received by the counter 63. The value of the counter 63 is corrected by the correction unit 64. The output of the counter 63 after correction by the correction unit 64 is fed back to the control processing unit 61.

[0036] The correction value includes a phase offset value determined based on the rotational position of the motor shaft 44a when a difference occurs between the rotational position of the motor shaft 44a measured by the motor encoder 44b and the actual rotational position of the motor shaft 44a, and a gain determined based on the amount of the difference. The phase offset value depends on the direction of eccentricity of the carriage motor 44. The amplitude depends on the magnitude of the eccentricity of the carriage motor 44.

[0037] Figure 6 is a block diagram illustrating the processing procedure for eccentricity correction. As shown in Figure 6, in the eccentricity correction process, the pulse signal output from the motor encoder 44b is counted by the counter 63. The count value 65 of the counter 63 is assumed to be pre-initialized by the origin detection function when the printer 10 is started. The count value 65 is input to the first adder 66, and the phase offset value 101, which has been determined in advance by the procedure in Figure 4, is added. The output of the first adder 66 is input to the remainder calculator 67. The remainder calculator 67 calculates the remainder obtained by dividing the number of input pulses by the number of pulses for one rotation of the motor shaft 44a (corresponding to the rotational position of the offset motor shaft 44a). The phase converter 68 converts the remainder obtained by the remainder calculator 67 into a sine value. In the multiplier 70, the value converted by the phase converter 68 is multiplied by the gain value 102, which has been determined in advance by the procedure in Figure 4, to obtain the correction value 100. In the second adder 71, a calculation is performed to subtract a correction value of 100 from the count value 65 of the motor encoder 44b, and this becomes the output of the second adder 71. The output of the second adder 71 is fed back to the control processing unit 61.

[0038] Figure 7 is a graph comparing the speed of the carriage 30 before and after correction. Graph G4 in Figure 7 represents the speed of the carriage 30 before correction. Graph G5 represents the speed of the carriage 30 after correction. Graph G6 represents the correction value. As mentioned above, the horizontal axis in Figure 7 represents the command position of the carriage 30. The vertical axis in Figure 7 represents the speed of the carriage 30 based on measurements by the linear encoder 45. As shown in Figure 7, in the printer 10 after speed correction of the carriage motor 44, the change in the speed of the carriage 30 is smaller compared to before correction. The range of existence for the vertical axis of graph G5 is narrower than the range of existence for the vertical axis of graph G4. From this, it can be seen that the method according to this embodiment suppresses fluctuations in the speed of the carriage 30 due to the position in the main scanning direction Y.

[0039] [Details of the second calculation step] The following section will explain in detail how to determine the phase difference and gain in the second calculation step S06.

[0040] Figure 8 is a flowchart detailing the second calculation step S06. As shown in Figure 8, in step S061 of the second calculation step S06, pulses emitted by the motor encoder 44b and the linear encoder 45 are acquired. The pulses from the motor encoder 44b and the linear encoder 45 are sampled at the same timing and at a constant period. Here, the pulses from the motor encoder 44b and the linear encoder 45 are sampled for multiple rotations of the motor shaft 44a, for example, 10 rotations. This improves the accuracy of the required phase difference and gain. However, the number of samples, sampling period, sampling interval, etc., of the pulses from the motor encoder 44b and the linear encoder 45 are not particularly limited.

[0041] In step S062, the measured values ​​of the motor encoder 44b and linear encoder 45 (each representing the rotational position of the motor shaft 44a) obtained in step S061 are converted from a time reference to a linear encoder 45 reference. Specifically, by obtaining the measured value of the motor encoder 44b at the timing when the measured value of the linear encoder 45 changes, the position of the motor shaft 44a based on the measurement of the motor encoder 44b is obtained relative to the position of the motor shaft 44a based on the measurement of the linear encoder 45.

[0042] In step S063, the resolution of the motor encoder 44b's measurement is adjusted to match the resolution of the linear encoder 45's measurement. Specifically, if the resolution of the motor encoder 44b is lower than the resolution of the linear encoder 45, the measurement of the motor encoder 44b is linearly interpolated. If the resolution of the motor encoder 44b is higher than the resolution of the linear encoder 45, step S063 is unnecessary.

[0043] In step S064, the deviation of the measured value of the motor encoder 44b from the measured value of the linear encoder 45 (hereinafter referred to as eccentricity) is determined for each sampling point of the linear encoder 45 data. Figure 9 is a graph showing the eccentricity of the carriage motor 44. The horizontal axis of Figure 9 represents the sampling points of the linear encoder 45 data. The vertical axis of Figure 9 represents the eccentricity. As shown in Figure 9, step S064 yields a graph G3A, which is a sine curve including offset (noise), as the graph of eccentricity.

[0044] In step S065, the offset included in the eccentricity (noise in the vertical axis direction in Figure 9) is removed. Specifically, for all sampling points shown on the horizontal axis of Figure 9, the eccentricity of points at a phase π / 2 earlier and later (if the phase of a given sampling point is θ, then the points at phase (θ-π / 2) and phase (θ+π / 2)) is obtained, and the average value of these is subtracted from the eccentricity of the sampling point. This removes the offset in the vertical axis direction in Figure 9.

[0045] Furthermore, in step S066, noise is reduced by calculating a moving average for all sampling points shown on the horizontal axis of Figure 9. Here, a moving average is calculated over a range of 1 / 4 of the period, i.e., an angle of π / 2. Figure 10 is a graph showing the eccentricity after noise removal. As shown in Figure 10, the noise reduction process in steps S065 and S066 results in the eccentricity graph becoming roughly a sine curve graph G3B.

[0046] In step S067, the gain and phase difference are calculated. In step S067, data from the constant-speed section where the carriage motor 44 is rotating at a constant speed are used. Data from the section where the carriage motor 44 is accelerating or decelerating are not used. Figure 11 is a graph showing the phase difference ΔP and gain ΔG in graph G3B, which shows the eccentricity after noise removal. As shown in Figure 10, the maximum eccentricity within the section in which the data is used is adopted as the gain ΔG. However, the absolute values ​​of the maximum and minimum values ​​of the eccentricity within the section in which the data is used may be determined, and the average of these absolute values ​​may be adopted as the gain ΔG.

[0047] As shown in Figure 11, the phase difference ΔP is taken from the phase (horizontal axis value) of point P0 where the eccentricity graph G3B first reaches zero deviation (zero on the vertical axis). Hereafter, the point where the eccentricity graph G3B first intersects the zero deviation line (horizontal axis) will also be called the zero-crossing point P0. The phase difference ΔP is the phase difference between the origin of the linear encoder 45 and the zero-crossing point P0. At the zero-crossing point P0, the derivative (rate of change) of the eccentricity is the largest. At the zero-crossing point P0, the slope of the graph G3B is the largest. In reality, the zero-crossing point P0 is the phase between a sampling point where the eccentricity is slightly positive and a sampling point where it is slightly negative. Therefore, the phase difference ΔP is more accurate when calculated at a point where the derivative of the eccentricity is large. In step S067, multiple phase differences ΔP are calculated within the interval, and the phase difference is calculated by averaging them.

[0048] In step S068, the phase difference obtained by moving the carriage 30 to the left and the phase difference obtained by moving the carriage 30 to the right are averaged. When the carriage 30 is moved to the left and when it is moved to the right, there may be a difference in the movement speed of the carriage 30 due to differences in mechanical conditions, such as the elongation of the belt 43. Therefore, in step S068, the phase difference obtained by moving the carriage 30 to the left and the phase difference obtained by moving the carriage 30 to the right are averaged.

[0049] [Other aspects of the second calculation step] However, the second calculation step S06 described above is merely a preferred example, and the second calculation step S06 is not limited thereto.

[0050] For example, in one preferred embodiment, the eccentricity of a predetermined number of sampling points is integrated (the area below or above a predetermined width on the horizontal axis is calculated), and the midpoint M1 of the range is found for the interval R1 in which the integral I was maximum (see Figure 12). In the example in Figure 12, the eccentricity of interval R1 is a positive value. The phase of this midpoint M1 is π / 2 if there is no phase difference in the eccentricity. Therefore, the phase difference ΔP can be used to determine the phase difference between the midpoint M1 and the point with phase π / 2. If the eccentricity of interval R1 is a negative value, the phase difference ΔP can be used to determine the phase difference ΔP between the midpoint M1 and the point with phase 3π / 2.

[0051] In another preferred embodiment, for example, the point where the derivative (rate of change) of the eccentricity is largest may be considered as the zero-crossing point P0.

[0052] In another preferred embodiment, two adjacent zero-crossing points P0A and P0B are determined, where the eccentricity shifts from positive to negative (here, zero-crossing points refer to the points where the eccentricity graph G3B intersects the zero deviation line (horizontal axis)). If there is no phase difference in the eccentricity, the phase of the midpoint M2 of the two zero-crossing points P0A and P0B is 3π / 2 (see Figure 13). In this case, the phase difference ΔP is the phase difference between the midpoint M2 and the phase 3π / 2 point. Note that the two zero-crossing points may also be two adjacent zero-crossing points where the eccentricity shifts from negative to positive.

[0053] In yet another preferred embodiment, the phase of a zero-crossing point P0 is determined from the direction in which the eccentricity shifts from positive to negative and from negative to positive. This improves the accuracy of the phase of the zero-crossing point P0.

[0054] In another preferred embodiment, the maximum point (the point where the slope shifts from positive to negative and the slope is zero) or minimum point (the point where the slope shifts from negative to positive and the slope is zero) of the eccentricity graph G3B is used. In this embodiment, if there is no phase difference in the eccentricity, the phase of the maximum point is π / 2 and the phase of the minimum point is 3π / 2. The phase difference ΔP is the phase difference between the maximum point and the point with phase π / 2, or the phase difference between the minimum point and the point with phase 3π / 2.

[0055] Thus, there are various methods for determining the phase difference between the phase of the motor shaft 44a based on the measurement of the motor encoder 44b and the phase of the motor shaft 44a based on the measurement of the linear encoder 45, and these methods are not particularly limited. Similarly, the method for determining the gain is not limited to the methods described above.

[0056] [Other embodiments] Preferred embodiments of the present invention have been described above. However, the embodiments described above are merely illustrative, and the present invention can be implemented in various other forms.

[0057] For example, in the embodiment described above, the correction of the rotational speed of the carriage motor 44 was not necessarily performed entirely by the printer 10, but it may be performed automatically by the printer 10. In that case, the printer 10 includes a print head 20, a carriage 30 on which the print head 20 is mounted and which travels in the main scanning direction Y, a carriage motor 44 that moves the carriage 30, a linear encoder 45 capable of measuring the position of the carriage 30 in the main scanning direction Y, and a control device 60. The carriage motor 44 includes a motor shaft 44a and a motor encoder 44b that measures the rotational position of the motor shaft 44a, and the rotational speed of the motor is controlled based on the rotational position of the motor shaft 44a measured by the motor encoder 44b.

[0058] Figure 14 is a block diagram of such a printer 10. As shown in Figure 14, the control device 60 here includes a travel control unit 161, a measurement control unit 162, a first calculation unit 163, a second calculation unit 164, a correction value determination unit 165, and a correction unit 166. The travel control unit 161 rotates the carriage motor 44 so that the rotational speed based on the measurement of the motor encoder 44b is constant, and moves the carriage 30. The measurement control unit 162 measures the position of the carriage 30 in the main scanning direction Y with the linear encoder 45 when the carriage 30 is moving under the control of the travel control unit 161. The first calculation unit 163 determines the rotational position of the motor shaft 44a (see Figure 2A) while the carriage 30 is moving, based on the measurement of the linear encoder 45. The second calculation unit 164 determines the difference between the rotational position of the motor shaft 44a based on the measurement by the motor encoder 44b and the rotational position of the motor shaft 44a determined by the first calculation unit 163, for multiple rotational positions over one or more rotations of the motor shaft 44a. Based on the difference calculated by the second calculation unit 164, the correction value determination unit 165 determines a correction value to be added to the rotational position of the motor shaft 44a measured by the motor encoder 44b, so as to reduce the change in the rotational speed of the motor shaft 44a within one rotation based on the measurement by the linear encoder 45. The correction unit 166 adds the correction value to the rotational position of the motor shaft 44a measured by the motor encoder 44b.

[0059] According to this printer 10, similar to the embodiment described above, it is possible to reduce the change in the speed of the carriage 30 caused by a change in the rotational speed of the carriage motor 44 within one rotation.

[0060] In the embodiment described above, the printer 10 was a type of printer in which the recording medium 5 is transported on a platen 15, but the type of printer is not limited. The printer may be a so-called flatbed type printer equipped with a flatbed on which the recording medium 5 is placed and moved.

[0061] The circuit, device, or process for adding a correction value, or in other words, the method for implementing the correction step S08, as described in Figure 6 of the above-described embodiment, is merely one preferred example. The process for adding a correction value to the rotational position of the motor shaft measured by the motor encoder is not limited to the process described above.

[0062] Unless otherwise specified, the embodiments of this invention are not limited to the present invention. [Explanation of symbols]

[0063] 10 Printers 20 printheads 30 Carriage 44 Carriage Motor 44a Motor shaft 44b Motor Encoder 45 Linear Encoders 60 Control device 161 Driving Control Unit 162 Measurement Control Unit 163 First Calculation Unit 164 Second Calculation Section 165 Correction Value Determination Unit 166 Correction section S01 Linear encoder counter initialization step S02 Preparation Steps S03 Running Step S04 Measurement Step S05 First calculation step S06 Second calculation step S07 Decision Step S08 Correction Step

Claims

1. A printer comprising a print head, a carriage on which the print head is mounted and which travels in a predetermined scanning direction, and a motor that moves the carriage, wherein a method for correcting the speed of the carriage, The motor comprises a motor shaft and a motor encoder for measuring the rotational position of the motor shaft, and the rotational speed is controlled based on the rotational position of the motor shaft measured by the motor encoder. A preparation step of preparing a linear encoder capable of measuring the position of the carriage in the scanning direction, A travel step in which the motor is rotated and the carriage is moved so that the rotational speed based on the measurement of the motor encoder is constant, A measurement step in which the position of the carriage in the scanning direction during the travel step is measured by the linear encoder, A first calculation step in which the rotational position of the motor shaft during the travel step is determined based on the measurement of the linear encoder, A second calculation step involves determining the difference between the rotational position of the motor shaft based on the measurement of the motor encoder and the rotational position of the motor shaft based on the measurement of the linear encoder at multiple rotational positions over one or more rotations of the motor shaft. A determination step in which, based on the difference calculated in the second calculation step, a correction value is determined to be added to the rotational position of the motor shaft measured by the motor encoder so as to reduce the change in the rotational speed of the motor shaft within one rotation based on the measurement of the linear encoder, A correction step of adding the correction value to the rotational position of the motor shaft measured by the motor encoder, A method that includes this.

2. The correction value includes a phase offset value determined based on the rotational position of the motor shaft when the difference occurs, and a gain determined based on the amount of the difference. The method according to claim 1.

3. The rotational speed of the motor during the aforementioned travel step is slower than the rotational speed of the motor during printing. The method according to claim 1.

4. print head and A carriage on which the print head is mounted and which travels in a predetermined scanning direction, A motor for moving the carriage, A linear encoder capable of measuring the position of the carriage in the scanning direction, A control device is provided, The motor comprises a motor shaft and a motor encoder for measuring the rotational position of the motor shaft, and the rotational speed is controlled based on the rotational position of the motor shaft measured by the motor encoder. The control device is A travel control unit that rotates the motor and moves the carriage so that the rotational speed based on the measurement of the motor encoder becomes constant, A measurement control unit measures the position of the carriage in the scanning direction using the linear encoder when the carriage is moving under the control of the aforementioned travel control unit, A first calculation unit that determines the rotational position of the motor shaft while the carriage is in motion based on the measurement of the linear encoder, A second calculation unit calculates the difference between the rotational position of the motor shaft based on the measurement of the motor encoder and the rotational position of the motor shaft determined by the first calculation unit, at multiple rotational positions over one or more rotations of the motor shaft. A correction value determination unit determines a correction value to be added to the rotational position of the motor shaft measured by the motor encoder, based on the difference calculated by the second calculation unit, so as to reduce the change in the rotational speed of the motor shaft within one rotation based on the measurement of the linear encoder. A printer comprising a correction unit that adds the correction value to the rotational position of the motor shaft measured by the motor encoder.

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