JP2003145877A - Serial printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a serial printer which can promptly stop a carriage when a desired encoder signal cannot be obtained from an optical type encoder. SOLUTION: A linear scale 41 is arranged parallel along a horizontal scanning direction so as to obtain position information of the carriage 13. The optical type encoder 42 set to the carriage 13 outputs the encoder signal obtained by reading the linear scale 41. A carriage scanning detection means 50 detects that the carriage 13 moves by a fixed distance, and outputs a signal at every time. An abnormality detection means 60 detects that the encoder signal is not normally outputted at the move time of the carriage 13 on the basis of the encoder signal and a signal from the carriage scanning detection means 50. A horizontal scanning motor control means 70 stops driving of a horizontal scanning motor 14 when the abnormality detection means 50 detects that the encoder signal is not normally outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a serial printer such as an ink jet printer which prints by moving a print head back and forth, and more particularly to a linear scale read by an optical encoder. The present invention relates to a serial printer that controls the speed and position of a carriage based on an encoder signal from the encoder.

[0002]

2. Description of the Related Art A serial printer such as an ink jet printer prints by moving a carriage equipped with a print head back and forth in the main scanning direction. As shown in FIG. 7, conventionally, a printer of this type has a print head 112, a carriage 113, and a main scanning motor 1.
14, the sub-scanning motor 115, and the main scanning drive mechanism 200
, Sub-scanning drive mechanism 300, and linear scale 410
An optical encoder 420, a main scanning motor control means 700 for controlling the main scanning motor 114, and a sub scanning motor control means 800 for controlling the sub scanning motor 115.

Nozzles for ejecting ink are arranged in the print head 112 along the sub-scanning direction (direction orthogonal to the main scanning direction). This print head 1
12 is mounted on the carriage 113. The carriage 113 is reciprocally moved in the main scanning direction by the main scanning drive mechanism 200. The main scanning drive mechanism 200 includes a belt 210 fixed to the carriage 113 and a drive pulley 2
20, the driven pulley 230, and the main scanning gear unit 24
Has 0 and. Here, the belt 210 is the drive pulley 2
20 and a driven pulley 230. The carriage 113 moves as the main scanning motor 114 moves the belt 210 via the main scanning gear unit 240. When the sub-scanning motor 115 is driven, the printer recording paper 2 is moved in the sub-scanning direction by the sub-scanning drive mechanism 300.

The linear scale 410 includes the carriage 11
3 for obtaining position information, and are arranged in parallel along the main scanning direction. An optical encoder 420 is attached to the carriage 113. The linear scale 410 is read by the optical encoder 420,
The optical encoder 420 outputs two encoder signals that are 90 ° out of phase with each other. The main scanning motor control means 700 drives the main scanning motor 114 based on the encoder signal from the optical encoder 420 to control the speed / position of the carriage 113.

[0005]

By the way, when the desired encoder signal cannot be obtained from the optical encoder for some reason, the speed and position of the carriage cannot be controlled properly.

There are several possible causes for the failure of the desired encoder signal from the optical encoder. For example, if the fixed position of the linear scale is displaced, the positional relationship between the linear scale and the light emitting surface / light receiving surface of the optical encoder becomes improper. Alternatively, stains such as ink drops or dust may be attached to the linear scale. In addition, when dirt is attached to the light emitting surface and the light receiving surface of the optical encoder, the encoder signal may not change even though the carriage is moving.

Particularly when the encoder signal from the optical encoder does not change over a wide range, the main scanning motor control means recognizes that the carriage is not moving and increases the driving torque of the main scanning motor. For this reason, the carriage may run away, and in the worst case, it may exceed the original scanning range and collide with the printer body constituent parts to damage the printer body. At this time, although the collision can be detected by detecting the overcurrent, the collision itself cannot be avoided.

As described above, conventionally, when the encoder signal is not input from the optical encoder, it is determined whether the carriage is actually moving or whether the carriage is moving but the encoder signal is not output from the optical encoder. It was difficult to do it immediately with an inexpensive device.

In particular, in recent years, the moving speed of the carriage has become faster and the weight of the carriage has increased due to the necessity of increasing the printing speed. Therefore, such runaway of the carriage is immediately detected and a countermeasure is taken. Required to do.

The present invention has been made based on the above circumstances, and when the desired encoder signal cannot be obtained from the optical encoder, the carriage is quickly stopped to prevent damage to the printer body due to the runaway of the carriage. An object is to provide a serial printer that can be minimized.

[0011]

According to a first aspect of the invention for achieving the above object, there is provided a print head for ejecting ink and a carriage for mounting the print head, and the carriage reciprocates. In a serial printer that forms an image on a recording medium by ejecting ink from the print head mounted on the carriage while moving, in order to obtain a scanning motor for moving the carriage and position information of the carriage Linear scales arranged in parallel along the moving direction of the carriage, and attached to the carriage,
An optical encoder that outputs an encoder signal obtained by reading the linear scale; a carriage scanning detection unit that detects that the carriage has moved a predetermined distance and outputs a signal each time the detection is performed; Encoder signal abnormality detecting means for detecting that the encoder signal is not normally output during movement of the carriage based on the encoder signal from the encoder and the signal from the carriage scanning detecting means, and the encoder signal abnormality detecting means. Scanning motor control means for stopping the drive of the scanning motor when it is detected by the means that the encoder signal is not normally output.

According to a second aspect of the present invention, in the serial printer according to the first aspect, the carriage scanning detection means includes a plate-shaped body that rotates in association with rotation of the scanning motor, and the plate-shaped body. At a position of the plate-shaped body separated from the center of rotation by a predetermined distance, one or a plurality of notches or protrusions formed at equal intervals along the rotation direction of the plate-shaped body, and the notch or There is a light emitting portion and a light receiving portion which are provided at positions corresponding to the protruding portions and are opposed to each other via the plate-shaped body, and the light emitted from the light emitting portion passes through the cutout portion. A signal is emitted when the light is received by the light receiving unit via the light receiving unit or when the light is not received by the light receiving unit blocked by the protrusion.

According to a third aspect of the present invention, in the serial printer according to the first or second aspect, the encoder signal abnormality detecting means uses the signal from the carriage scanning detecting means as a trigger signal, and 1+ (n-1). ) From the time when the m-th (m is a predetermined natural number, n = 1, 2, 3, ...) Trigger signal is sent until the 1 + nm-th trigger signal is sent, It has a counter for counting the number of pulses of the encoder signal from the encoder, and outputs a signal indicating that the encoder signal is not normally output when the count value of the counter is less than or equal to a predetermined reference value. It is what

Further, the invention according to claim 4 is the invention according to claim 1,
The serial printer according to 2 or 3, further comprising display means for displaying a warning to that effect when the encoder signal abnormality detection means detects that the encoder signal is not normally output. Is.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a serial printer which is an embodiment of the present invention, FIG. 2 is a schematic side view of a carriage scanning detection means in the serial printer, and FIG. 3 is a schematic plan view of a disk of the carriage scanning detection means. .

As shown in FIG. 1, the serial printer of this embodiment includes a platen 11, a print head 12, and
The carriage 13, the main scanning motor 14, the sub scanning motor 15, the main scanning drive mechanism 20, and the sub scanning drive mechanism 30.
, Linear scale 41, optical encoder 42,
The carriage scanning detection unit 50, the encoder signal abnormality detection unit 60, the main scanning motor control unit 70, the sub scanning motor control unit 80, the CPU (not shown), and the display unit (not shown) are provided. .

The platen 11 is for mounting the printer recording paper 2 on its upper surface. The printer recording paper 2 is recorded on the platen 11 by the print head 12. The sub-scanning drive mechanism 30 includes a sub-scanning gear unit 31.
And a paper feed roller 32. When the sub-scanning motor 15 rotates the paper feed roller 32 via the sub-scanning gear unit 31, the printer recording paper 2 is conveyed in the sub-scanning direction (vertical direction in FIG. 1) and moves on the platen 11. Moving.

The main scanning drive mechanism 20 has a belt 21 fixed to the carriage 13, a drive pulley 22, a driven pulley 23, and a main scanning gear unit 24. Here, the belt 21 is suspended between a drive pulley 22 and a driven pulley 23. This belt 21 is used for the main scanning motor 1
Move left and right by 4. As a result, the carriage 13
Can reciprocate through the belt 21 in a direction (main scanning direction) orthogonal to the sub scanning direction.

The carriage 13 has a print head 12
Is installed. Therefore, the print head 12
The carriage 13 can move integrally with the carriage 13 along the main scanning direction. The print head 12 has a large number of nozzles on its lower surface, and ejects minute ink droplets from the ejection openings of each nozzle. These nozzles are arranged in a substantially straight line along the sub-scanning direction.

The main scanning motor control means 70 controls the main scanning motor 14, while the sub scanning motor control means 80 controls the sub scanning motor 15. CP
U centralizes the control of each unit of the serial printer. For example, the CPU sends a signal for controlling the movement of the carriage 13 to the main scanning motor control means 70,
A signal for controlling the conveyance of the printer recording paper 2 is sent to the sub-scanning motor control means 80. Further, the CPU creates a signal for controlling the ink ejection of the print head 12 based on the image data, and sends it to a print head drive unit (not shown). Further, the CPU causes the display means to display predetermined information and warnings.

When executing the printing operation, the CPU
First, the operation of the carriage 13 is controlled to move the print head 12 along the main scanning direction. At this time, C
When the PU sends a signal to the print head driver, ink droplets are ejected from the nozzles of the print head 12. As a result, an image for one band is formed on the printer recording paper 2. Next, the CPU controls the operation of the carriage 13 to return the print head 12 to a predetermined position, and at the same time, moves the printer recording paper 2 by one band along the sub-scanning direction. An image is formed on the entire printer recording paper 2 by alternately repeating the operation of ejecting the ink and the operation of conveying the printer recording paper 2.

The linear scale 41 is for obtaining the position information of the carriage 13, and is arranged in parallel along the main scanning direction. This linear scale 41 has
A large number of slits are formed at regular intervals. For example, such slits are formed at 300 lines per inch.

An optical encoder 42 is attached to the carriage 13. The optical encoder 42 has a light emitting unit and a light receiving unit. The light emitting section and the light receiving section are arranged at positions facing each other via the linear scale 41. When the light emitted from the light emitting section is received by the light receiving section through the slit of the linear scale 41, the optical encoder 42 outputs an encoder signal to the main scanning motor control means 70 and the encoder signal abnormality detection means 60. On the other hand, the light emitted from the light emitting unit is linear scale 4
If it is blocked by 1 and does not reach the light receiving portion, the optical encoder 42 does not output an encoder signal. In this way, the linear scale 41 is read by the optical encoder 42. The encoder signal is the speed of the carriage 13,
Used to know position. Main scanning motor control means 7
0 controls the speed / position of the carriage 13 based on the encoder signal from the optical encoder 42. In the present embodiment, as the optical encoder 42, an encoder that outputs two encoder signals of A phase and B phase which are 90 ° out of phase is used. By using these two encoder signals, it is possible to increase the resolution four times and to know the moving direction of the carriage 13, that is, whether the carriage 13 is moving from right to left or from left to right. You can

The carriage scanning detecting means 50 detects whether or not the carriage 13 is moving. As shown in FIG. 2, a disc (plate-like body) 51 and an optical sensor 52 are provided.
With. As shown in FIG. 3, the disk 51 has two slits (notches) 51 from the peripheral edge toward the center.
a is formed. Here, the two slits 51a are formed at positions facing each other. Also, the disc 51
The gear 51 b attached to the rotating shaft of the above gear meshes with the gear in the main scanning gear unit 24. Therefore, when the main scanning motor 14 rotates, the carriage 13 moves, and at the same time as the rotation of the main scanning motor 14, the disk 5 moves.
1 also rotates.

In general, the slits formed on the disk 51 may have any shape and may have any number. However, when forming a plurality of slits, it is necessary to arrange them at equal intervals along the circumference of the disk 51.

As shown in FIG. 2, the optical sensor 52 has a light emitting portion 52a and a light receiving portion 52b. The light emitting portion 52a and the light receiving portion 52b are arranged at positions facing each other with the end portion of the disk 51 interposed therebetween. When the light emitted from the light emitting portion 52a is received by the light receiving portion 52b through the slit 51a of the disk 51, the optical sensor 52 outputs a signal. On the other hand, if the light emitted from the light emitting portion 52a is blocked by the disk 51 and does not reach the light receiving portion 52b, the optical sensor 52 does not output a signal. In particular, in this embodiment, the slit 51a is formed into the disk 51.
Since it is formed at equal intervals along the circumference of the optical sensor 5,
2 outputs a signal each time the slit 51a is detected, that is, each time the carriage 13 moves by a fixed distance. Therefore, if the signal from the optical sensor 52 changes with time, the carriage 13 is moving, while if the signal from the optical sensor 52 does not change with time, the carriage 13 is stopped. It will be. The output signal from the optical sensor 52 (carriage scanning detection means 50) is sent to the encoder signal abnormality detection means 60.

The encoder signal abnormality detecting means 60 detects that the encoder signal is not normally output from the optical encoder 42, that is, that the encoder signal is abnormal, and the A-phase counter 61 and the B-phase counter 61. And a counter 62. The A-phase counter 61 counts the number of pulses of the A-phase encoder signal sent from the optical encoder 42, and the B-phase counter 62 counts the number of pulses of the B-phase encoder signal sent from the optical encoder 42. It is a thing. In particular,
Each of the counters 61, 62 uses the output signal from the optical sensor 52 as a trigger signal and triggers the 1+ (n-1) mth (m is a predetermined natural number, n = 1, 2, 3, ...) Trigger. The number of pulses of the encoder signal is counted from the time the signal is sent to the time the 1 + nmth trigger signal is sent. Here, in the present embodiment, for example, m =
1, that is, each of the counters 61 and 62 counts the number of encoder signal pulses from when a certain trigger signal is sent to when the next trigger signal is sent. The encoder signal abnormality detection means 60 determines whether or not the count value counted by each of the counters 61 and 62 is less than or equal to a predetermined reference value. When the count values of both counters 61 and 62 exceed the reference value, it is determined that the encoder signal is normally output, and one of the counters 61 and 62 is output.
If the count value of is less than or equal to the reference value, it is determined that the encoder signal is not normally output.

When the encoder signal abnormality detecting means 60 detects that the encoder signal is not output normally, it outputs a signal to that effect to the main scanning motor control means 70 and the CP.
Output to U. Then, the main scanning motor control means 70
When receiving such a signal, the main scanning motor 14 promptly
Stop driving. On the other hand, when the CPU receives the signal, it causes the display means to display a warning that the operation of the carriage has stopped because the encoder signal is abnormal. still,
As a matter of course, the encoder signal abnormality detecting means 60
May output a signal to that effect only when the encoder signal is normally output, and may not output the signal when the encoder signal is not normally output.

Next, the abnormality detection operation of the encoder signal in the serial printer of this embodiment will be described.
FIG. 4 is a flow chart for explaining the abnormality detection operation of the encoder signal in the serial printer of this embodiment.

For example, when the printing operation is started, the encoder signal abnormality detecting means 60 first clears the count value of the A-phase counter 61 and the count value of the B-phase counter 62 (S01). Next, the main scanning motor control means 70
In order to realize the printing operation, the main scanning motor 14 is driven to start the movement of the carriage 13 (S02). As a result, the carriage 13 moves along the main scanning direction.

When the carriage 13 starts moving, an encoder signal is output from the optical encoder 42. 5 and 6 show examples of waveforms of the A-phase and B-phase encoder signals, the trigger signal, and the signals from the A-phase and B-phase counters 61 and 62. These figures show carriage 13
This is an example of the case where is moving at a constant speed. In FIG. 5, each pulse is regularly output at regular intervals for each of the A-phase encoder signal and the B-phase encoder signal. That is, the encoder signal is normally output from the optical encoder 42. On the other hand, in FIG. 6, although the carriage 13 is moving, the A phase and B phase encoder signals are not output for a certain period of time. That is, the encoder signal is not output normally.

Next, the encoder signal abnormality detecting means 60
Determines whether a trigger signal has been sent from the carriage scanning detection means 50 (S03). That is, the encoder signal abnormality detection means 60 waits for the trigger signal to change from the state in which the trigger signal has not changed. When the trigger signal changes, it is determined that the trigger signal has been sent, and the process proceeds to S04. At S04, the A-phase counter 61 and B of the encoder signal abnormality detecting means 60 are detected.
The phase counters 62 start counting operations for the number of pulses of the A-phase encoder signal and the number of pulses of the B-phase encoder signal, respectively.

After that, the encoder signal abnormality detecting means 60
Judges whether or not a signal for stopping the carriage 13 or a signal for reversing the scanning direction of the carriage 13 is sent from the main scanning motor control means 70 (S05). When the carriage 13 is stopped, the trigger signal does not change with time. On the other hand, carriage 1
If the scanning direction of 3 is reversed, the time intervals at which the trigger signal changes become irregular. Therefore, when these signals are sent, the A-phase counter 61 and the B-phase counter 62 stop counting the number of pulses of the encoder signal (S06). Then, the process proceeds to S01. That is, the abnormality detection operation of the encoder signal is performed from the beginning.

On the other hand, when the signal for stopping the carriage 13 and the signal for reversing the scanning direction of the carriage 13 are not sent in S05, the encoder signal abnormality detecting means 60 determines the carriage scanning detecting means. It is determined whether or not the next trigger signal is sent from 50 (S07). If the next trigger signal has not been sent, the process proceeds to S05. On the other hand, if the next trigger signal is sent, the process proceeds to S08.

In S08, the encoder signal abnormality detecting means 60 determines whether the count value of each of the A-phase counter 61 and the B-phase counter 62 is less than or equal to a predetermined reference value n. When it is determined that the count values of both counters 61 and 62 exceed the reference value n, the encoder signal abnormality detection means 60 causes the encoder signal abnormality detection means 60 from the time when the trigger signal is sent to the time when the next trigger signal is sent, that is,
While the carriage 13 moves by a certain distance, it is recognized that the optical encoder 42 outputs an encoder signal of a predetermined number of pulses or more, and it is determined that the encoder signal is normally output. After that, the encoder signal abnormality detection means 60 detects the count value of the A phase counter 61 and the B value.
The count value of the phase counter 62 is cleared (S09), and S
The processing moves to 04.

On the other hand, if it is determined in S08 that the count value of one of the counters 61 and 62 is less than or equal to the reference value n, the encoder signal abnormality detecting means 60 causes the optical signal to be detected while the carriage 13 moves by a certain distance. It is recognized that the number of pulses of the encoder signal output from the expression encoder 42 is too small, and it is determined that the encoder signal is abnormal.

In the examples of FIGS. 5 and 6, the signal from the A-phase counter 61 and the signal from the B-phase counter 62 are turned off when the trigger signal changes to on, and the counters are turned off. When the count value of exceeds the reference value n, it changes from off to on. That is, FIG.
In the example of FIG. 6, the processing of S07 in the flow of FIG. 4 is omitted, and the encoder signal abnormality detection means 60 does not determine the presence or absence of the next trigger signal, and the count values of the counters 61 and 62 are reference values. It is decided to judge whether it exceeds n. In this case, it is checked whether the encoder signal is normally output by checking whether the signals from the counters 61 and 62 are on or off at the timing when the next trigger signal is input. You can judge.

In FIG. 5, when the next trigger signal is input, the signals from the counters 61 and 62 are on, so it is determined that the encoder signal is normally output. On the other hand, in FIG. 6, when the next trigger signal is input, since the signals from the counters 61 and 62 are off, it is determined that the encoder signal is abnormal.

When it is determined in S08 that the encoder signal is not normally output, the encoder signal abnormality detecting means 60 sends a signal to that effect to the main scanning motor control means 7
0 and send to CPU. Upon receiving such a signal, the main scanning motor control means 70 stops driving the main scanning motor 14 and stops the movement of the carriage 13 (S10). Further, the CPU causes the display means to display a warning that the movement of the carriage 13 has been stopped because the encoder signal is not normally output (S11). This is the end of the processing flow of FIG.

In the serial printer of this embodiment, by providing the carriage scanning detection means and the encoder signal abnormality detection means, if the desired encoder signal cannot be obtained from the optical encoder for some reason,
Since the abnormality of the encoder signal can be immediately detected and the carriage can be stopped quickly, damage to the printer body due to the runaway of the carriage can be minimized.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the gist thereof.

In the above embodiment, the encoder signal abnormality detecting means is provided with the A-phase counter for counting the number of pulses of the A-phase encoder signal and the B-phase counter for counting the number of pulses of the B-phase encoder signal. Although the case has been described, for example, only one of the counters may be provided. However, an abnormality may occur in only one of the A-phase encoder signal and the B-phase encoder signal. Therefore, in order to accurately detect the abnormality in the encoder signal, it is necessary to use the same method as described in the above embodiment. It is desirable to have two counters.

Further, in the above embodiment, the case where the carriage scanning detection means having the disk having the slit, the light emitting portion and the light receiving portion is used is explained. Instead of the body, for example, a square plate-shaped body may be used. Further, instead of forming slits in these plate-shaped bodies, at the positions of the plate-shaped bodies that are separated from the center of rotation of the plate-shaped bodies by a predetermined distance, they are evenly spaced along the rotation direction of the plate-shaped bodies. Alternatively, a plurality of protrusions may be formed. However, when the protruding portion is formed, the carriage scanning detection means emits a signal when the light emitted from the light emitting portion is blocked by the protruding portion and is not received by the light receiving portion.

[0044]

As described above, the serial printer according to the present invention detects the movement of the carriage by a predetermined distance and outputs a signal each time the detection is performed, and a carriage scanning detection means and an optical encoder. Encoder signal abnormality detecting means for detecting that the encoder signal is not normally output during movement of the carriage, based on the encoder signal and the signal from the carriage scanning detecting means,
And a scanning motor control means for stopping the driving of the scanning motor when the encoder signal abnormality detection means detects that the encoder signal is not normally output.
As a result, when the desired encoder signal cannot be obtained from the optical encoder for some reason, an abnormality in the encoder signal can be immediately detected and the carriage can be stopped immediately. The damage to the body can be minimized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a serial printer that is an embodiment of the present invention.

FIG. 2 is a schematic side view of carriage scanning detection means in the serial printer.

FIG. 3 is a schematic plan view of a disk of the carriage scanning detection means.

FIG. 4 is a flowchart for explaining an abnormality detection operation of an encoder signal in the serial printer of this embodiment.

FIG. 5 is a diagram showing the waveform of each signal when the encoder signal is normal.

FIG. 6 is a diagram showing the waveform of each signal when the encoder signal is abnormal.

FIG. 7 is a schematic configuration diagram of a conventional serial printer.

[Explanation of symbols]

2 ... Printer recording paper, 11 ... Platen, 12 ... Print head, 13 ... Carriage, 14 ... Main scanning motor, 15 ... Sub scanning motor, 20 ... Main scanning drive Mechanism, 21 ... Belt, 22 ... Drive pulley, 23 ... Driven pulley, 24 ... Main scanning gear unit, 30 ... Sub-scanning drive mechanism, 31 ... Sub-scanning gear unit, 32 ... Paper feed roller, 41 ... Linear scale, 42 ... Optical encoder, 50 ... Carriage scanning detection means, 51 ...
-Disc, 51a ... Slit, 51b ... Gear, 52 ...
-Optical sensor, 52a ... Light emitting part, 52b ... Light receiving part, 6
0 ... Encoder signal abnormality detection means, 61 ... A phase counter, 62 ... B phase counter, 70 ... Main scanning motor control means, 80 ... Sub scanning motor control means

Claims (5)

[Claims] 1. A print head for ejecting ink,
A serial printer having a carriage on which the print head is mounted, wherein the carriage is moved back and forth to form an image on a recording medium by ejecting ink from the print head mounted on the carriage. A scanning motor for moving the carriage, a linear scale arranged in parallel along the moving direction of the carriage to obtain position information of the carriage, and a linear scale attached to the carriage and obtained by reading the linear scale. An optical encoder that outputs an encoder signal, and detects that the carriage has moved a certain distance,
Based on the carriage scanning detection unit that outputs a signal each time the detection is performed, and the encoder signal from the optical encoder and the signal from the carriage scanning detection unit, the encoder signal is normally output when the carriage moves. An encoder signal abnormality detecting means for detecting that the encoder signal is not normally output, and a scanning motor control means for stopping the driving of the scanning motor when the encoder signal abnormality detecting means detects that the encoder signal is not normally output. A serial printer comprising: 2. The carriage scanning detection means is provided at a position of the plate-like body that rotates in association with the rotation of the scanning motor and a position of the plate-like body that is separated from the center of rotation of the plate-like body by a predetermined distance. One or a plurality of notches or protrusions formed at equal intervals along the rotation direction of the plate-like body, and a position corresponding to the notch or the protrusions at the plate-like body It has a light emitting portion and a light receiving portion provided at positions facing each other, and when the light emitted from the light emitting portion is received by the light receiving portion through the cutout portion or is blocked by the protruding portion. 2. The serial printer according to claim 1, wherein the serial printer emits a signal when no light is received by the light receiving unit. 3. The encoder signal abnormality detecting means uses the signal from the carriage scanning detecting means as a trigger signal, and is the 1+ (n-1) mth (m is a predetermined natural number, n = 1, 2, 3). , ...) from the time the trigger signal is sent to the time the 1 + nmth trigger signal is sent, the counter has a counter that counts the number of pulses of the encoder signal from the optical encoder. 3. The serial printer according to claim 1, wherein when the count value is less than or equal to a predetermined reference value, a signal indicating that the encoder signal is not normally output is output. 4. When the encoder signal abnormality detection means detects that the encoder signal is not normally output, the display means is provided for displaying a warning to that effect. Or the serial printer described in 3. 5. The serial printer according to claim 1, 2, 3, or 4, wherein the optical encoder outputs two encoder signals that are 90 ° out of phase with each other.