Photosensor driving device and printing device

Abstract

To provide a photosensor driving device and a printing device capable of reducing the number of ports required for a control part at using a plurality of photosensors.SOLUTION: A photosensor driving device includes: a plurality of photosensors having light emitting elements and light receiving elements; and a control part having an output port connected to the light emitting elements of the plurality of photosensors in common and a plurality of input ports respectively connected to the light receiving elements of the plurality of photosensors, for sequentially outputting, to each of the light emitting elements, signals having duty ratios according to each of the plurality of photosensors through the output ports, inhibiting input from the photosensors which are not subject to detection among the plurality of photosensors during a period when the signals are output, and inputting the output of the light receiving element obtained by light emission of the light emitting element subject to detection among the plurality of photosensors through the input ports.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a photosensor driving device and a printing device. [Background technology]

[0002] BACKGROUND ART Conventionally, there are known techniques for using a photosensor as a means for detecting paper or black marks in a printer, and techniques for controlling the light-emitting current of the photosensor by a PWM (Pulse Width Modulation) method (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-248182 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-114324 Summary of the Invention [Problem to be solved by the invention]

[0004] When multiple photosensors are used, an MCU (Micro Controller Unit) must be connected to the multiple photosensors and have output ports for outputting signals to each photosensor and input ports for receiving output values ​​from each photosensor. Therefore, as the number of photosensors used increases, the number of output and input ports required for the MCU also increases, which can strain the MCU's resources. This can also force the selection of a relatively expensive MCU with a large number of ports.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a photosensor driving device and a printing device that can reduce the number of ports required for a control unit when using multiple photosensors. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the photosensor driving device disclosed in the specification is characterized in that it comprises a plurality of photosensors each having a light-emitting element and a light-receiving element, an output port commonly connected to the light-emitting elements of the plurality of photosensors, and a plurality of input ports respectively connected to the light-receiving elements of the plurality of photosensors, and outputs a signal having a duty ratio corresponding to each of the plurality of photosensors to each of the light-emitting elements in sequence via the output port, and during the period in which the signal is being output, prohibits input from photosensors among the plurality of photosensors that are not the detection target, and inputs the output of the light-receiving element obtained by the emission of the light-emitting element among the plurality of photosensors that is the detection target via the input port.

[0007] In order to achieve the above-mentioned object, the photosensor driving device disclosed in the specification is characterized by comprising a plurality of photosensors each having a light-emitting element and a light-receiving element, a plurality of output ports each connected to the light-emitting element of the plurality of photosensors, and an input port commonly connected to the light-receiving elements of the plurality of photosensors, and a control unit that outputs signals having duty ratios corresponding to each of the plurality of photosensors to each of the light-emitting elements in sequence via the plurality of output ports, and treats data input from the input port during the period in which the signal is being output as the output of the photosensor being detected that is outputting the signal. [Effects of the Invention]

[0008] According to the present invention, when a plurality of photosensors are used, the number of ports required for the control unit can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a configuration diagram of a printing device including a photosensor driving device according to a first embodiment. [Figure 2] FIG. 1 is a configuration diagram of a photosensor driving device according to a first embodiment. [Figure 3]10 is a diagram showing the relationship between a signal output from an MCU and outputs from a plurality of photosensors. FIG. [Figure 4] 4A is a diagram showing the relationship between the output voltages of multiple photosensors and the output read timing when power is supplied to the multiple photosensors in sequence by switching between them, and FIG. 4B is a diagram showing the relationship between the output voltages of multiple photosensors and the output read timing when power is supplied to the multiple photosensors at all times. [Figure 5] 10 is a flowchart showing a process for adjusting a duty ratio. [Figure 6] FIG. 10 is a configuration diagram of a photosensor driving device according to a second embodiment. [Figure 7] 10 is a diagram showing the relationship between a signal output from an MCU and outputs from a plurality of photosensors. FIG. [Figure 8] FIG. 10 is a configuration diagram of a photosensor driving device according to a modified example of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] (First embodiment) 1 is a configuration diagram of a printing device equipped with a photosensor driving device according to the first embodiment. The printing device 1 is, for example, a thermal printer that prints on roll paper 2, but the type of printer is not important, and it may be an inkjet printer or laser printer, etc.

[0012] The printing device 1 includes a control board 3, a thermal head 4, a platen roller 5, a transport path 6, and photosensors 20 and 30 (first and second photosensors). The control board 3 includes an MCU (Micro Controller Unit) 10 (controller) that controls the overall operation of the printing device 1. The MCU 10 is electrically connected to the thermal head 4, photosensors 20 and 30, and a motor (not shown) that transports the roll paper 2.

[0013] The thermal head 4 is a component that uses Joule heat generated by passing current to cause a thermally reactive material in the roll paper 2 (thermal paper) to react and print. The platen roller 5 is a roller used as a component responsible for feeding the paper and pressing it against the thermal head 4. The transport path 6 is a path for transporting the roll paper 2. The photosensor 20 is a sensor for reading marks on, for example, the back side of the roll paper 2 (the side opposite the printed surface), and the photosensor 30 is a sensor for reading marks on, for example, the front side (printed surface) of the roll paper 2 and detecting the presence or absence of the roll paper 2.

[0014] The photosensors 20 and 30 are, for example, reflective photosensors, but may also be transmissive photosensors. In the example of Fig. 1, the photosensors 20 and 30 are reflective photosensors and are therefore arranged to face the roll paper 2. The photosensors 20 and 30 face each other across the transport path 6, but the arrangement of the photosensors 20 and 30 is not limited to the example of Fig. 1. The printing device 1 may also be equipped with three or more photosensors.

[0015] When the photosensors 20, 30 are transmission type photosensors, the photosensors 20, 30 are arranged on the transport path 6 so that the roll paper passes between the light emitting element and the light receiving element of each of the photosensors 20, 30.

[0016] Fig. 2 is a configuration diagram of a photosensor driving device according to the first embodiment. Fig. 3 is a diagram showing the relationship between the signal output from MCU 10 and the outputs from photosensors 20 and 30. Note that hatched portion 25 in Fig. 3 indicates that MCU 10 prohibits input of output voltage from photosensor 20, and hatched portion 26 indicates that MCU 10 prohibits input of output voltage from photosensor 30.

[0017] As shown in FIG. 2, the photosensor driving device 100 according to the first embodiment includes an MCU 10, photosensors 20 and 30, light-emitting current adjusting resistors 41 and 42, and sensor output detecting resistors 43 and 44. The MCU 10, light-emitting current adjusting resistors 41 and 42, and sensor output detecting resistors 43 and 44 are mounted on a control board 3 shown in FIG. 1. The MCU 10 includes an AD conversion unit 11, a comparison unit 12, an output port 13, a first input port 14A, and a second input port 14B. The photosensor 20 includes an LED 21 (first light-emitting element) and a phototransistor 22 (first light-receiving element). The photosensor 30 includes an LED 31 (second light-emitting element) and a phototransistor 32 (second light-receiving element).

[0018] A power supply that supplies power to photosensors 20 and 30 is connected to the collectors of phototransistor 22 and phototransistor 32. The emitter of phototransistor 22 is connected to first input port 14A and one end of sensor output detection resistor 43. The emitter of phototransistor 32 is connected to second input port 14B and one end of sensor output detection resistor 44. The other ends of sensor output detection resistors 43 and 44 are connected to ground (earthed).

[0019] The output port 13 is connected to the anodes of the LEDs 21 and 31. The cathode of the LED 21 is connected to one end of a light-emitting current adjusting resistor 41, and the other end of the light-emitting current adjusting resistor 41 is grounded. The cathode of the LED 31 is connected to one end of a light-emitting current adjusting resistor 42, and the other end of the light-emitting current adjusting resistor 42 is grounded.

[0020] The light-emitting current adjusting resistors 41 and 42 are resistors for adjusting the current flowing through the LEDs 21 and 31, respectively, or in other words, for adjusting the light emission intensity of the LEDs 21 and 31. When the resistance values ​​of the light-emitting current adjusting resistors 41 and 42 are reduced, the current flowing through the LEDs 21 and 31 increases, and the light emission intensity of the LEDs 21 and 31 increases. When the resistance values ​​of the light-emitting current adjusting resistors 41 and 42 are increased, the current flowing through the LEDs 21 and 31 decreases, and the light emission intensity of the LEDs 21 and 31 decreases.

[0021] The sensor output detection resistors 43 and 44 convert the current flowing between the collector and emitter of the phototransistors 22 and 32, respectively, into a voltage and input it to the AD conversion unit 11. In other words, these resistors are used to adjust the detection sensitivity for the output current of the phototransistors 22 and 32. When the resistance values ​​of the sensor output detection resistors 43 and 44 are reduced, the voltage input to the AD conversion unit 11 decreases.

[0022] Power consumption can be reduced by setting the resistance values ​​of the sensor output detection resistors 43 and 44 and the light emission current adjustment resistors 41 and 42 to be large within a range that does not exceed the characteristics of the photosensors 20 and 30, that is, within a range in which the current flowing through the LEDs 21 and 31 and the current flowing between the collector and emitter of the phototransistors 22 and 32 do not exceed the values ​​specified in the data sheets of the photosensors 20 and 30.

[0023] As shown in Fig. 3, MCU 10 sequentially outputs a first signal having a first duty ratio and a second signal having a second duty ratio to photosensors 20 and 30, respectively, via output port 13. The first signal having the first duty ratio is a PWM (Pulse Width Modulation) signal for controlling the current flowing through photosensor 20, and the second signal having the second duty ratio is a PWM signal for controlling the current flowing through photosensor 30. Note that since the first duty ratio and the second duty ratio are used to adjust the outputs of photosensors 20 and 30, respectively, the first duty ratio and the second duty ratio may be the same or different from each other. While Fig. 3 shows an example in which the first duty ratio is larger than the second duty ratio, the first duty ratio may be smaller than the second duty ratio.

[0024] The LEDs 21 and 31 emit light when they receive a first signal having a first duty ratio. In the phototransistor 22, a current (photocurrent) corresponding to the incident light from the LED 21 becomes the base current of the phototransistor 22, and an output current flows between the collector and emitter of the phototransistor 22. The output voltage of the photosensor 20, which is generated by the current flowing through the sensor output detection resistor 43, is input to the first input port 14A. In the phototransistor 32, a current (photocurrent) corresponding to the incident light from the LED 31 becomes the base current of the phototransistor 32, and an output current flows between the collector and emitter of the phototransistor 32. The output voltage of the photosensor 30, which is generated by the current flowing through the sensor output detection resistor 44, is input to the second input port 14B.

[0025] The AD conversion unit 11 of the MCU 10 performs AD conversion on the output voltages of the photosensors 20 and 30. The comparison unit 12 compares the output voltages of the photosensors 20 and 30 after AD conversion with a predetermined threshold, and detects the presence or absence of paper or a black mark depending on whether the output voltage of the photosensor 20 after AD conversion exceeds the predetermined threshold. For example, when a white portion of paper is read, the output voltages of the photosensors 20 and 30 become a high voltage value (a value close to the power supply voltage), and when a black portion of paper or a part of a housing when no paper is present is read, the output voltages of the photosensors 20 and 30 become a low voltage value (a value close to 0 V). Therefore, the comparison unit 12 can detect the presence or absence of paper or a black mark depending on whether the output voltage of the photosensors 20 and 30 after AD conversion exceeds the predetermined threshold.

[0026] As described above, when the MCU 10 outputs the first signal having the first duty ratio from the output port 13, the LEDs 21 and 31 simultaneously emit light. Since the first signal having the first duty ratio is a signal for controlling the current flowing through the photosensor 20, the output voltage of the photosensor 30 is not necessary.

[0027] 3, while the MCU 10 is outputting the first signal having the first duty ratio, the MCU 10 prohibits input from the second input port 14B (see hatched portion 26), and inputs the output voltage of the phototransistor 22 obtained by light emission of the LED 21 via the first input port 14A. While the MCU 10 is outputting the first signal having the first duty ratio, the MCU 10 may receive and discard the input from the second input port 14B.

[0028] Similarly, when the MCU 10 outputs a second signal having a second duty ratio from the output port 13, the LEDs 21 and 31 simultaneously emit light. Since the second signal having the second duty ratio is a signal for controlling the current flowing through the photosensor 30, the output voltage of the photosensor 20 is not necessary.

[0029] 3, during the period when the MCU 10 is outputting the second signal having the second duty ratio, the MCU 10 prohibits input from the first input port 14A (see hatched portion 25), and inputs the output voltage of the phototransistor 32 obtained by the light emission of the LED 31 via the second input port 14B. The MCU 10 may receive and discard the input from the first input port 14A during the period when the MCU 10 is outputting the second signal having the second duty ratio. As described above, since the input from the second input port 14B is prohibited during the period when the first signal is output, and the input from the first input port 14A is prohibited during the period when the MCU 10 is outputting the second signal, the MCU 10 can appropriately control the multiple photosensors even if it has only one output port connected to the multiple photosensors.

[0030] 3, the output voltage of photosensor 20 may be read within the period during which the first signal having the first duty ratio is output. Furthermore, the output voltage of photosensor 20 may be read multiple times within the period during which the first signal having the first duty ratio is output. For example, the average value of the multiple read values ​​may be used as the output voltage of photosensor 20.

[0031] Similarly, the output voltage of photosensor 30 may be read during the period in which the second signal having the second duty ratio is output. Furthermore, the output voltage of photosensor 30 may be read multiple times during the period in which the second signal having the second duty ratio is output. For example, the average value of the multiple read values ​​may be used as the output voltage of photosensor 30.

[0032] Fig. 4(A) is a diagram showing the relationship between the output voltages of photosensors 20 and 30 and the output read timings of photosensors 20 and 30 when LED21 and LED31 are connected to separate output ports and switched in sequence. Fig. 4(B) is a diagram showing the relationship between the output voltages of photosensors 20 and 30 and the output read timings of photosensors 20 and 30 when the output of output port 13 is constantly supplied to LED21 and LED31.

[0033] 4A, the LED drive by the output port is switched from LED 21 to LED 31. In this case, it becomes necessary to wait for the rise of the output voltage of photosensors 20 and 30 due to a delay in signal amplification of phototransistors 22 and 32. Since the outputs of photosensors 20 and 30 are read after the output voltages of photosensors 20 and 30 have stabilized, the timing at which reading of photosensors 20 and 30 begins is delayed, and it is also difficult to shorten the interval between reading of photosensor 20 and reading of photosensor 30.

[0034] In contrast, in the first embodiment, LED 21 and LED 31 are simultaneously energized when reading the outputs of phototransistors 22 and 32, i.e., the output voltages of photosensors 20 and 30. In this case, LED 21 and LED 31 are not switched, and therefore, as shown in FIG. 4B , reading by photosensor 30 can be initiated at an earlier timing than when energization to LEDs 21 and 31 is switched, regardless of the delay in signal amplification of phototransistors 22 and 32. This shortens the interval between reading by photosensor 20 and reading by photosensor 30, and enables the reading process by photosensors 20 and 30 to be completed earlier than when energization to LEDs 21 and 31 is switched. Furthermore, because reading by photosensor 30 can be initiated at an earlier timing, it is also possible to read the output voltage of photosensor 30 multiple times and use the average of the read values.

[0035] 5 is a flowchart showing the duty ratio adjustment process, in which the first duty ratio and the second duty ratio are used as the duty ratios.

[0036] First, paper with a fixed reflectance is set in the printing device 1 (S1). Next, the MCU 10 causes the photosensors 20 and 30 to emit light (S2) and reads the output voltages of the photosensors 20 and 30 (S3). The MCU 10 compares the output voltages of the photosensors 20 and 30 with the reference voltages of the photosensors 20 and 30 (S4). The reference voltages of the photosensors 20 and 30 are values ​​that are set in advance in the MCU 10.

[0037] If the output voltage of the photosensors 20, 30 is lower than the reference voltage of the photosensors 20, 30 in S4, the MCU 10 increases the duty ratio (S5) and repeats the process of S5 until the output voltage of the photosensors 20, 30 matches the reference voltage of the photosensors 20, 30.

[0038] If the output voltage of the photosensors 20, 30 is higher than the reference voltage of the photosensors 20, 30 in S4, the MCU 10 reduces the duty ratio (S6) and repeats the process of S6 until the output voltage of the photosensors 20, 30 matches the reference voltage of the photosensors 20, 30.

[0039] If the output voltages of the photosensors 20 and 30 match the reference voltages of the photosensors 20 and 30 in S4, the MCU 10 stores the duty ratio in a memory (not shown) within the MCU 10 (S7), and ends this process.

[0040] In this way, by adjusting the first duty ratio of the first signal and the second duty ratio of the second signal, it is possible to finely adjust the light emission intensities of the LEDs 21 and 31. In the photosensor driving device 100 according to the first embodiment, the light emission intensities of the LEDs 21 and 31 are adjusted by the resistance values ​​of the light emission current adjustment resistors 41 and 42, and the light emission intensities of the LEDs 21 and 31 that cannot be fully adjusted by the resistance values ​​of the light emission current adjustment resistors 41 and 42 are finely adjusted by the first duty ratio of the first signal and the second duty ratio of the second signal supplied to the LEDs 21 and 31.

[0041] According to the first embodiment, the MCU 10 outputs a first signal having a first duty ratio and a second signal having a second duty ratio to the photosensors 20 and 30, respectively, sequentially via one output port 13. Then, while the MCU 10 is outputting the first signal, it prohibits input from the second input port 14B and inputs the output of the phototransistor 22 obtained by the emission of the LED 21 via the first input port 14A, and while it is outputting the second signal, it prohibits input from the first input port 14A and inputs the output of the phototransistor 32 obtained by the emission of the LED 31 via the second input port 14B.

[0042] This allows the multiple photosensors 20, 30 to be controlled by the first signal and the second signal output in sequence from one output port 13, and the multiple input ports 14A, 14B to detect the outputs from the multiple photosensors 20, 30, respectively, thereby reducing the number of ports of the MCU 10 when using multiple photosensors 20, 30. Also, an inexpensive MCU with a small number of ports can be used as the MCU 10.

[0043] (Second embodiment) The second embodiment differs from the first embodiment in the number of output ports and the number of input ports of the MCU 10.

[0044] Fig. 6 is a configuration diagram of a photosensor driving device according to the second embodiment. Fig. 7 is a diagram showing the relationship between the signal output from MCU 10 and the outputs from photosensors 20 and 30.

[0045] 6, a photosensor driving device 101 according to the second embodiment includes an MCU 10, photosensors 20 and 30, light-emitting current adjusting resistors 41 and 42, and a sensor output detecting resistor 43. The MCU 10 includes an AD conversion unit 11, a comparison unit 12, a first output port 13A, a second output port 13B, and an input port 14. The photosensors 20 and 30 according to the second embodiment are similar to the photosensors 20 and 30 according to the first embodiment. The processing and functions of the AD conversion unit 11 and comparison unit 12 of the MCU 10 according to the second embodiment are similar to the processing and functions of the AD conversion unit 11 and comparison unit 12 of the MCU 10 according to the first embodiment.

[0046] A power supply that supplies voltage to photosensors 20 and 30 is connected to the collectors of phototransistor 22 and phototransistor 32. The emitter of phototransistor 22 is connected to input port 14 and one end of sensor output detection resistor 43. The emitter of phototransistor 32 is connected to input port 14 and one end of sensor output detection resistor 43. The other end of sensor output detection resistor 43 is connected to ground (earthed).

[0047] The first output port 13A is connected to the anode of the LED 21. The cathode of the LED 21 is connected to one end of a light-emitting current adjustment resistor 41, and the other end of the light-emitting current adjustment resistor 41 is grounded. The second output port 13B is connected to the anode of the LED 31. The cathode of the LED 31 is connected to one end of a light-emitting current adjustment resistor 42, and the other end of the light-emitting current adjustment resistor 42 is grounded.

[0048] The light emitting current adjusting resistors 41 and 42 of the second embodiment are similar to the light emitting current adjusting resistors 41 and 42 of the first embodiment. The sensor output detecting resistor 43 of the second embodiment is similar to the sensor output detecting resistor 43 of the first embodiment.

[0049] The LED 21 emits light when it receives a first signal having a first duty ratio. In the phototransistor 22, a current (photocurrent) corresponding to the incident light from the LED 21 becomes the base current of the phototransistor 22, and an output current flows between the collector and emitter of the phototransistor 22. The output voltage of the photosensor 20, which is generated by the current flowing through the phototransistor 22 and the sensor output detection resistor 43, is input to the input port 14.

[0050] The LED 31 emits light when it receives a second signal having a second duty ratio. In the phototransistor 32, a current (photocurrent) corresponding to the incident light from the LED 31 becomes the base current of the phototransistor 32, and an output current flows between the collector and emitter of the phototransistor 32. The output voltage of the photosensor 30, which is generated by the current flowing through the phototransistor 32 and the sensor output detection resistor 43, is input to the input port 14.

[0051] 7, the MCU 10 outputs a first signal having a first duty ratio to the photosensor 20 via the first output port 13A, and outputs a second signal having a second duty ratio to the photosensor 30 via the second output port 13B at a timing that does not overlap with the output period of the first signal. In this way, the period during which the first signal having the first duty ratio is output does not overlap with the period during which the second signal having the second duty ratio is output, so the MCU 10 can acquire the output voltages of the multiple photosensors 20, 30 via the single input port 14. Note that the first and second signals of the second embodiment are PWM signals, similar to the first and second signals of the first embodiment.

[0052] According to the second embodiment, the MCU 10 outputs a first signal having a first duty ratio and a second signal having a second duty ratio to the LEDs 21 and 31, respectively, via the first output port 13A and the second output port 13B. During the period in which the MCU 10 is outputting the first signal, the MCU 10 inputs the output of the phototransistor 22 obtained by the emission of light from the LED 21 via the input port 14, and during the period in which the MCU 10 is outputting the second signal, the MCU 10 inputs the output of the phototransistor 32 obtained by the emission of light from the LED 31 via the input port 14.

[0053] This allows the multiple photosensors 20, 30 to be controlled by the first signal and the second signal output from the multiple output ports 13A, 13B, respectively, and allows the outputs from the multiple photosensors 20, 30 to be detected by a single input port 14, thereby reducing the number of ports of the MCU 10 when using multiple photosensors 20, 30. Also, an inexpensive MCU with a small number of ports can be used as the MCU 10.

[0054] Fig. 8 is a configuration diagram of a photosensor driving device according to a modification of the second embodiment. Photosensor driving device 102 in Fig. 8 differs from photosensor driving device 101 in Fig. 6 in that two light-emitting current adjustment resistors 41 and 42 are combined into one common light-emitting current adjustment resistor 41. The rest of the configuration is the same as that of photosensor driving device 101 in Fig. 6.

[0055] When the maximum and minimum values ​​of the output current of the phototransistor 22 and the output current of the phototransistor 32 are within a range of ±50% of the standard value of the output current predetermined as the characteristics of the phototransistor 22 and the phototransistor 32, respectively, the light-emitting current adjustment resistor connected between the LED 21 and the ground and another light-emitting current adjustment resistor connected between the LED 31 and the ground are commonized to one light-emitting current adjustment resistor 41.

[0056] This eliminates the need to connect separate light-emitting current adjusting resistors between LED 21 and ground and between LED 31 and ground, thereby reducing the manufacturing cost of the photosensor driving device. The light-emitting intensity of LEDs 21 and 31, which cannot be fully adjusted by the resistance value of light-emitting current adjusting resistor 41, can be fine-tuned by the first duty ratio of the first signal and the second duty ratio of the second signal.

[0057] The present invention is not limited to the above-described embodiment, and can be implemented in various modified forms without departing from the spirit and scope of the invention. [Explanation of symbols]

[0058] 1 Printing device, 10 MCU, 11 AD conversion unit, 12 Comparison unit, 13 output port, 13A first output port, 13B second output port, 14 input port, 14A first input port, 14B second input port, 20, 30 Photo sensor, 21, 31 LED, 22, 32 Phototransistor, 41, 42 Light-emitting current adjustment resistor, 43, 44 Sensor output detection resistor

Claims

1. a plurality of photosensors each having a light emitting element and a light receiving element; an output port commonly connected to the light-emitting elements of the plurality of photosensors, and a plurality of input ports respectively connected to the light-receiving elements of the plurality of photosensors; outputting signals having duty ratios corresponding to the respective plurality of photosensors to the respective light-emitting elements via the output port in sequence; a control unit that prohibits input from a photosensor that is not a detection target among the plurality of photosensors during a period in which the signal is being output, and inputs an output from the light-receiving element obtained by light emission from the light-emitting element that is a detection target among the plurality of photosensors via the input port; A photosensor driving device comprising:

2. a plurality of photosensors each having a light emitting element and a light receiving element; a plurality of output ports respectively connected to the light-emitting elements of the plurality of photosensors, and an input port commonly connected to the light-receiving elements of the plurality of photosensors; outputting signals having duty ratios corresponding to the plurality of photosensors to the light-emitting elements in sequence via the plurality of output ports; a control unit that converts data input from the input port during a period when the signal is being output into an output of the photosensor that is the detection target and is outputting the signal; A photosensor driving device comprising:

3. When the maximum and minimum values ​​of the output currents of the plurality of light receiving elements are within a range of ±50% of a standard value of the output current predetermined as a characteristic of the light receiving elements, a resistor connected between the plurality of light emitting elements and ground 3. The photosensor driving device according to claim 2, further comprising:

4. A printing device comprising the photosensor driving device according to claim 1 or 2.

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