JP2020116825A - Sensor control device and image formation apparatus - Google Patents

Abstract

To provide a sensor control device which can suppress the influence due to the noise even when the noise is generated in the supply voltage in such a configuration that a plurality of sensors are connected in series.SOLUTION: A sensor control device includes a main substrate 200, first sensor 131 to third sensor 133 connected in series to the main substrate 200 and a terminal unit 134 which is connected to the third sensor 133. The main substrate 200 causes the first sensor 131 to third sensor 133 to perform the detection operation in the order from the upstream side by applying the first voltage and the second voltage alternately, and to perform the detection operation in the order from the first sensor 131 again when acquiring the detection result of the third sensor 133. The main substrate 200 determines that any of the first sensor 131 to third sensor 133 operates erroneously when acquiring the terminal level generated by the terminal unit 134.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to a control technology of a sensor provided in the image forming apparatus.

An image forming apparatus and an automatic document feeder (ADF: Auto Document Feeder) have a large number of sensors for controlling internal devices. For example, the image forming apparatus is equipped with various sensors such as a sensor used to detect the presence or absence of a sheet, a sensor used to detect the sheet conveyance position, and a sensor used to detect the opening/closing of the exterior cover of the apparatus. The image forming apparatus controls the sheet conveyance by operating an internal device based on the detection result of the sensor. Therefore, a large number of sensors arranged at various positions in the apparatus and a controller that obtains the detection result of the sensor and controls the conveyance of the sheet are connected via a large number of cables.

An increase in the number of cables and connectors hinders the miniaturization of the entire device and causes an increase in cost. For this reason, a technique has been proposed in which a plurality of sensors are connected in series to a controller to reduce the number of cables and the number of connectors (Patent Document 1). Patent Document 1 proposes a configuration in which a plurality of sensors are connected in series. Each sensor includes a light emitting unit and a light receiving unit, and detects the presence or absence of a sheet and the opening/closing of a cover depending on whether there is a shield between the light emitting unit and the light receiving unit. Each sensor is provided with a resistor having a different resistance value, and for example, a detection result at the time of sheet detection is represented by a different voltage value for each sensor according to the resistance value. Therefore, the controller can determine from which sensor the detection result is output.

JP, 2008-59161, A

In a configuration in which a plurality of sensors are connected in series and individually operated, the power supply voltage is applied from the controller to the most upstream sensor connected in series. The controller, for example, switches the voltage value of the power supply voltage applied to the most upstream sensor to sequentially operate each sensor in time division from the most upstream sensor to the downstream side. During operation, each sensor operates with the power supply voltage supplied from the upstream side, and supplies the power supply voltage to the sensor connected to the downstream side after the operation. To this end, each sensor is provided with a control unit that operates with the power supply voltage and performs detection operation control and supply power voltage supply operation control to the downstream sensor. Since this control unit operates by the power supply voltage, if noise occurs in the power supply voltage, normal operation control may not be performed.

The present invention has been made in view of the above problems, and a sensor control device capable of suppressing the influence of noise even when noise occurs in a power supply voltage in a configuration in which a plurality of sensors are connected in series. The purpose is to provide.

The sensor control device of the present invention is connected to a control means, a plurality of sensors connected in series to the control means, and a downstream side of the plurality of sensors with the control means side as an upstream side. Terminating means, and each of the plurality of sensors performs a detection operation when a first voltage is applied from the control means, and the first sensor is applied after the first voltage is applied from the control means. When a second voltage different from the one voltage is applied, the voltage applied from the control means is supplied to the sensor or the terminating means connected in the subsequent stage, and the terminating means detects the detection results of the plurality of sensors. Generates a termination level that is a different voltage value, and the control unit repeatedly applies the first voltage and the second voltage to sequentially perform the detection operation from the sensor on the upstream side to detect each sensor. It is characterized in that the results are sequentially acquired, and the malfunction of the sensor is judged based on the detection status of the terminal level.

According to the present invention, a configuration in which a plurality of sensors are connected in series can suppress the influence of noise even when noise occurs in the voltage (power supply voltage) supplied from the control unit.

FIG. 1 is a configuration diagram of an image forming apparatus. The block diagram of a sensor control apparatus. FIG. 4 is a functional block diagram for carrying out sheet conveyance control. The flowchart showing operation control processing. The timing chart at the time of operation control. The timing chart at the time of operation control. The flowchart showing operation control processing. The timing chart at the time of operation control. The timing chart at the time of operation control. The block diagram of a sensor control apparatus. The flowchart showing operation control processing. The timing chart at the time of operation control of a 1st sensor. The timing chart at the time of operation control. The timing chart at the time of operation control of a 1st sensor. The timing chart at the time of operation control. The flowchart showing operation control processing. The timing chart at the time of operation control. The timing chart at the time of operation control.

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

(First embodiment)
FIG. 1 is a configuration diagram of an image forming apparatus including the sensor control device of the present embodiment. The image forming apparatus 100 is an electrophotographic system. The image forming apparatus 100 includes a photoconductor 101, a charger 102, a potential sensor 103, an exposure device 104, a developing device 105, a transfer unit 106, a cleaner 107, and a fixing device 108 for forming an image. The image forming apparatus 100 includes a sheet feeding cassette 120 that stores the sheet 110, a sheet feeding roller 122, and conveyance rollers 124 and 126 for feeding the sheet 110. The operation of the image forming apparatus 100 is controlled by a controller (not shown).

The paper feed cassette 120 includes a sensor 131 that detects the sheets 110 that are stored. A plurality of sensors 132 and 133 are provided at predetermined intervals on the transport path along which the sheet 110 is fed. The image forming apparatus 100 includes a stepping motor 121 to drive the paper feed roller 122. The image forming apparatus 100 includes a stepping motor 123 for driving the conveying roller 124. The image forming apparatus 100 includes a stepping motor 125 to drive the conveyance roller 126.

The photoconductor 101 is rotated clockwise in the drawing. The charger 102 uniformly charges the surface of the rotating photoconductor 101. The exposure device 104 forms an electrostatic latent image according to the image signal on the surface of the photoconductor 101 by exposing the photoconductor 101 whose surface is uniformly charged according to the image signal. The developing device 105 develops the electrostatic latent image to form a toner image on the surface of the photoconductor 101. The potential sensor 103 is provided between the exposure device 104 and the developing device 105 in order to measure the potential of the electrostatic latent image. The toner image formed on the surface of the photoconductor 101 is transferred to the sheet 110 by the transfer unit 106. The transfer residual toner remaining on the photoconductor 101 after the transfer is collected by the cleaner 107. The sheet 110 onto which the toner image has been transferred has the toner image fixed by the fixing device 108 and is ejected from the image forming apparatus 100. In this way, an image-formed product is obtained.

The feeding operation of the sheet 110 will be described. When starting the feeding operation, the controller detects the presence or absence of the sheet 110 in the paper feed cassette 120 by the sensor 131. When the sheet 110 is present in the sheet feeding cassette 120, the controller starts feeding the sheet 110 stored in the sheet feeding cassette 120 by the sheet feeding roller 122 according to the instruction of the sheet feeding operation. The controller drives the paper feed roller 122 with the stepping motor 121. The sheet feeding roller 122 conveys the sheets 110 one by one from the sheet feeding cassette 120 to the conveying roller 124. The sensor 132 is provided in the transport path between the paper feed roller 122 and the transport roller 124. The sensor 132 detects whether or not the sheet 110 has passed a detection position on the conveyance path from the paper feed roller 122 to the conveyance roller 124. The controller detects, based on the detection result of the sensor 132, whether or not the sheet 110 has passed the detection position within a predetermined timing. At this time, if the passage of the sheet 110 at the detection position cannot be detected within the predetermined timing, the controller stops the rotation of the stepping motor 121 and temporarily stops the feeding operation.

When the sensor 132 detects the sheet 110, the controller causes the stepping motor 123 to rotationally drive the carry roller 124. The conveying roller 124 rotates to convey the sheet 110 conveyed from the paper feeding roller 122 to the conveying roller 126. The sensor 133 is provided on the transport path between the transport rollers 124 and 126. The sensor 133 detects whether or not the sheet 110 has passed a detection position on the conveyance path from the conveyance roller 124 to the conveyance roller 126. The controller detects, based on the detection result of the sensor 133, whether the sheet 110 has passed the detection position within a predetermined timing. At this time, if the passage of the detection position of the sheet 110 cannot be detected within the predetermined timing, the controller stops the rotation of the stepping motor 123 and temporarily stops the feeding operation.

When the sensor 133 detects the sheet 110, the controller causes the stepping motor 125 to rotationally drive the carry roller 126. The conveyance roller 126 rotates to convey the sheet 110 conveyed from the conveyance roller 124 to the transfer unit 106. The timing at which the transport roller 124 transports the sheet 110 to the transfer unit 106 is adjusted according to the timing at which the toner image formed on the photoconductor 101 is transported to the transfer unit 106. As a result, the sheet 110 and the toner image formed on the photosensitive member 101 overlap and pass through the transfer portion 106, and the toner image is transferred to a predetermined position on the sheet 110. The controller may control the conveyance speed of the sheet 110 by the conveyance rollers 126 so that the toner image on the photoconductor 101 overlaps the sheet 110 and passes through the transfer unit 106.

As described above, the controller individually controls the drive of the stepping motors 121, 123, and 125 based on the detection results of the sensors 131 to 133, thereby controlling the rotational drive of each roller to convey the sheet 110. .. The controller, the sensors 131 to 133, the stepping motors 121, 123 and 125, the paper feed roller 122, and the transport rollers 124 and 126 form a sheet transport device.

The sensors 131 to 133 of the present embodiment are configured by photo interrupters, for example. In this case, each of the sensors 131 to 133 includes a light emitting unit (for example, LED: Light Emitting Diode) and a light receiving unit (for example, a phototransistor) that receives light emitted from the light emitting unit. The presence or absence of the sheet 110 is detected by, for example, the sensors 132 and 133 provided on the transport path by pressing a shield provided at the detection position of the transport path on the sheet 110 to shield the optical path between the LED and the phototransistor with the shield. Can be detected. Further, the sensors 132 and 133 are arranged, for example, such that the LED and the phototransistor are opposed to each other with the transport path interposed therebetween, and detect the presence or absence of the sheet 110 by blocking the optical path when the sheet 110 passes through the transport path. It may be configured. Alternatively, the light from the LED may be reflected by the sheet 110 in the transport path to form an optical path to the phototransistor.

The sensor 131 provided in the paper feeding cassette 120 can detect the sheet 110 by forming an optical path to the phototransistor by reflecting the light of the LED by the sheet 110, for example. Further, the sensor 131 has a configuration in which the LED and the phototransistor are arranged to face each other with the mounting position of the sheet 110 interposed therebetween, and the optical path is blocked when the sheet 110 is present to detect the presence or absence of the sheet 110. May be.

(controller)
FIG. 2 is a configuration diagram of a sensor control device including a main board 200 included in the controller and a sensor. In the following description, the sensor 131 will be referred to as the first sensor 131. The sensor 132 is described as the second sensor 132. The sensor 133 is described as the third sensor 133. The main board 200 controls the detection operations of the first sensor 131 to the third sensor 133 and acquires the detection results of these.

The first sensor 131 to the third sensor 133 are connected to the main board 200 in series. The first sensor 131 to the third sensor 133 are connected in order of the first sensor 131, the second sensor 132, and the third sensor 133 from the upstream side with the main board 200 side as the upstream side. The first sensor 131 to the third sensor 133 have the same internal configuration. The terminating unit 134 is connected to the subsequent stage of the third sensor 133 provided on the most downstream side. The terminal unit 134 is provided to detect a malfunction of each sensor 131, 132, 133.

The main board 200 and the first sensor 131, the first sensor 131 and the second sensor 132, the second sensor 132 and the third sensor 133, the third sensor 133 and the termination unit 134 are connected by different power supply lines and signal lines, respectively. .. A power supply voltage is applied from the main board 200 to the first sensor 131 to the third sensor 133 and the terminal unit 134 by the power supply line. The detection results of the first sensor 131 to the third sensor 133 and the voltage generated by the terminal unit 134 are input to the main board 200 through the signal line. The main board 200, the first sensor 131, the second sensor 132, the third sensor 133, and the termination unit 134 are grounded in common.

The main board 200 includes a CPU (Central Processing Unit) 201 and a power supply switching unit 202. The CPU 201 controls at least the operations of the first sensor 131 to the third sensor 133. The power supply switching unit 202 switches the power supply voltage applied to the first sensor 131 to the third sensor 133 and the terminating unit 134. The power supply switching unit 202 applies power supply voltages of three different voltage values to the first sensor 131 to the third sensor 133 and the terminating unit 134. In the present embodiment, the power supply switching unit 202 has three types of power supply voltages to be applied to the first sensor 131 to the third sensor 133 and the terminal unit 134, which are 0 [V], 3.3 [V], and 5 [V]. Switch. The main board 200 includes a pull-up resistor 204 to obtain the detection results of the first sensor 131 to the third sensor 133 and the voltage generated by the termination unit 134. A predetermined voltage (here, 3.3 [V]) is applied to one end of the pull-up resistor 204. The main board 200 includes a connector 203 for connecting to the first sensor 131 via a power line and a signal line.

The first sensor 131 includes a connector 210a, a voltage detection unit 211a, a power cutoff unit 212a, an LED 213a, a phototransistor 214a, and an LED control unit 215a. The connector 210a is connected to the main board 200 via a power supply line and a signal line, and is also connected to the second sensor 132 provided on the downstream side via another power supply line and another signal line.

The voltage detection unit 211a detects a power supply voltage applied from the main board 200, and outputs a control signal for controlling conduction of the power cutoff unit 212a and the LED control unit 215a according to the voltage value. That is, the voltage detection unit 211a functions as a control unit that controls the operation of the first sensor 131 according to the voltage value of the power supply voltage. Details of the operation of the voltage detection unit 211a will be described later.

The power cutoff unit 212a has a switch element in a supply path that supplies a power supply voltage to a sensor (second sensor 132) in the subsequent stage. The power cutoff unit 212a switches the supply state of the power supply voltage applied from the main board 200 to the second sensor 132 in the subsequent stage by switching the switch element according to the control signal acquired from the voltage detection unit 211a. The switch element is, for example, a MOS (Metal Oxide Semiconductor) type FET (Field Effect Transistor). When the control signal (voltage value) from the voltage detection unit 211a becomes lower than the power supply voltage applied from the main board 200 by the gate threshold voltage (for example, 1 [V]), the FET is cut off, and the power supply cutoff unit 212a. Does not supply the power supply voltage to the second sensor 132 in the subsequent stage.

The LED 213a is a light emitting unit that emits light by a current flowing according to a power supply voltage applied from the main board 200. The phototransistor 214a is a light receiving unit that receives and operates the light emitted from the LED 213a. In this embodiment, the phototransistor 214a becomes conductive by receiving light. The collector terminal of the phototransistor 214a is connected to the pull-up resistor 204 of the main substrate 200 and the CPU 201 by a signal line. When the phototransistor 214a is conductive, the ground voltage (0 [V]) is input to the CPU 201 as the detection result of the first sensor 131. When the phototransistor 214a is in the cutoff state, the voltage (3.3 [V]) applied to the pull-up resistor 204 is input to the CPU 201 as the detection result of the first sensor 131. The phototransistor 214a itself becomes high impedance in the cutoff state. In this way, the CPU 201 can detect conduction and interruption (open state) of the phototransistor 214a. The phototransistor 214a enters a cutoff state by blocking the light from the LED 213a by the sheet 110, for example. The CPU 201 can detect the sheet 110 by detecting the cutoff state.

The LED control unit 215a has a switch element in the application path of the power supply voltage to the LED 213a. The LED control unit 215a switches the application state of the power supply voltage applied from the main board 200 to the LED 213a by switching the switch element according to the control signal acquired from the voltage detection unit 211a. The switch element is, for example, a MOS type FET. When the voltage of the control signal from the voltage detection unit 211a becomes lower than the power supply voltage applied from the main substrate 200 by the gate threshold voltage (for example, 1 [V]), the FET is cut off and the LED control unit 215a No power supply voltage is applied to the LED 213a. The LED 213a does not emit light because no current flows when the power supply voltage is not applied.

The operation of the voltage detection unit 211a will be described. The voltage detection unit 211a detects the rise and fall of the power supply voltage applied from the main board 200, for example, with a threshold value of 4 [V]. However, the voltage detection unit 211a does not detect the rise when the voltage is changed from 0 [V] to 4 [V] or more when the power is turned on. The voltage detection unit 211a enters the “first state” after the power supply voltage is turned on. The voltage detection unit 211a maintains the first state until the applied power supply voltage once exceeds 4 [V] (for example, 5 [V]) and then detects a falling edge that crosses 4 [V]. When the applied power supply voltage decreases from 5 [V] to 3.3 [V], the voltage detection unit 211a detects the falling edge over 4 [V]. In this case, the voltage detection unit 211a is in the "second state". The voltage detection unit 211a in the second state maintains the second state regardless of the power supply voltage until the power supply voltage applied from the main board 200 becomes 0 [V]. Note that the power supply voltage applied from the main board 200 becomes 0 [V] is called “initialization”. The initialized voltage detector 211a is in the first state.

In the case of the first state, the voltage detection unit 211a controls the power cutoff unit 212a to be in the cutoff state in which the power supply voltage is not supplied to the downstream second sensor 132. When in the second state, the voltage detection unit 211a controls the power cutoff unit 212a to be in a conductive state in which the power supply voltage is supplied to the second sensor 132 located downstream. That is, the voltage detection unit 211a controls the power cutoff unit 212a to be in the conductive state in response to the power supply voltage falling from 5 [V] to 3.3 [V]. The voltage detection unit 211a maintains the power cutoff unit 212a in the conductive state until the power supply voltage becomes 0 [V].

In the case of the first state, the voltage detection unit 211a controls the LED control unit 215a so that the LED control unit 215a is in a conductive state in which a current is passed through the LED 213a to emit light. In the conductive state, the LED 213a emits light based on the power supply voltage. In the case of the second state, the voltage detection unit 211a controls the LED control unit 215a to be in a cutoff state in which the current to the LED 213a is cut off and turned off. That is, the voltage detection unit 211a controls the LED control unit 215a to turn off the LED 213a in response to the power supply voltage falling from 5 [V] to 3.3 [V]. Even when the power supply voltage rises from 3.3 [V] to 5 [V], the LED control unit 215a maintains the cutoff state. Therefore, the LED 213a remains off.

The connector 210b of the second sensor 132 is connected to the upstream first sensor 131 via a power supply line and a signal line, and also connected to the downstream third sensor 133 to another power supply line and another signal line. Connected via. The second sensor 132 includes a voltage detection unit 211b, a power cutoff unit 212b, an LED 213b, a phototransistor 214b, and an LED control unit 215b. The operation of each unit is the same as the operation of each corresponding unit of the first sensor 131, and a description thereof will be omitted.

The collector terminal of the phototransistor 214b of the second sensor 132 is connected to the signal line connecting the collector terminal of the phototransistor 214a and the connector 210a at the contact a in the first sensor 131. Therefore, the output value of the signal line connecting the first sensor 131 and the main substrate 200 can be changed based on the output value of the phototransistor 214b.

The connector 210c of the third sensor 133 is connected to the second sensor 132 on the upstream side via a power supply line and a signal line, and also connects another power supply line and another signal line to the termination unit 134 provided on the downstream side. Connected through. The third sensor 133 includes a voltage detection unit 211c, a power cutoff unit 212c, an LED 213c, a phototransistor 214c, and an LED control unit 215c. The operation of each unit is the same as the operation of each corresponding unit of the first sensor 131, and a description thereof will be omitted.

The collector terminal of the phototransistor 214c of the third sensor 133 is connected to the signal line connecting the collector terminal of the phototransistor 214b of the second sensor 132 and the connector 210b at the contact b in the second sensor 132. The signal line connecting the collector terminal of the phototransistor 214b and the connector 210b is connected to the signal line connecting the collector terminal of the phototransistor 214a and the connector 210a as described above. Therefore, the output value of the signal line connecting the first sensor 131 and the main substrate 200 can be changed based on the output value of the phototransistor 214c.

Unlike the configuration of the first sensor 131 to the third sensor 133, the terminating unit 134 includes a resistance element for resistively dividing the power supply voltage supplied from the power cutoff unit 212c of the third sensor 133. The termination unit 134 of this embodiment includes a termination resistor 216 and a termination resistor 217 as such resistance elements. The termination unit 134 generates a voltage obtained by resistively dividing the power supply voltage by the pull-up resistor 204, the termination resistor 216, and the termination resistor 217 of the main board 200. Specifically, the terminating unit 134 divides the power supply voltage by the combined resistance of the pull-up resistor 204 and the terminating resistor 216 and the terminating resistor 217. The resistance-divided voltage value of the power supply voltage is supplied to the signal line connecting the collector terminal of the phototransistor 214c of the third sensor 133 and the connector 210c at the contact c of the third sensor 133. Therefore, the output value of the signal line connecting the first sensor 131 and the main board 200 may be a voltage value divided by resistance. In addition, the voltage value generated by resistance division by the pull-up resistor 204 and the terminating resistors 216 and 217 is a voltage value determined by the driving states of the phototransistors 214a to 214c of the first sensor 131 to the third sensor 133. This is a value different from (Detection result). The resistance values of the termination resistors 216 and 217 are set so as to generate a voltage having such a voltage value. Therefore, the CPU 201 can identify whether the voltage value acquired via the signal line is the detection result of the first sensor 131 to the third sensor 133 or the voltage value of the voltage generated by the terminal unit 134. Has become.

Each sensor can have the same interface for connecting to the main board 200 or another sensor regardless of the connection location (upstream, downstream, or midway) in the series connection. Therefore, it is possible to use the same sensor (same external shape, same internal circuit) for all the sensors. Each sensor does not require connection management between the sensor and the sensor or change the outer shape of each sensor, and has an inexpensive configuration that does not require a complicated control circuit such as packet communication. In this embodiment, three sensors are connected in series, but the number of sensors can be further increased by the same control.

By connecting the power supply lines and the signal lines in this way, it is possible to reduce the number of power supply lines and signal lines that connect the main substrate 200 and the plurality of sensors (the first sensor 131 to the third sensor 133). Therefore, it becomes possible to reduce the number of cables and the number of connectors, and to suppress the cost and the component management cost. Further, the number of pins and the occupied area of the connector 203 of the main board 200 can be reduced, and the cost can be reduced.

(Sheet conveyance control)
FIG. 3 is a functional block diagram for the main substrate 200 to control the conveyance of the sheet 110. The main board 200 functions as a power supply switching control unit 301, a sensor level detection unit 302, a recording unit 303, and a sheet conveyance control unit 304. Each function is realized, for example, by the CPU 201 executing a predetermined control program.

The power supply switching control unit 301 transmits a switching signal for switching the voltage value of the output power supply voltage to the power supply switching unit 202. The sensor level detection unit 302 detects the detection results of the first sensor 131 to the third sensor 133 and the voltage generated by the termination unit 134. The detection results of the first sensor 131 to the third sensor 133 detected by the sensor level detection unit 302 are recorded in the recording unit 303. The recording unit 303 temporarily records the detection results of the first sensor 131 to the third sensor 133 in a register or the like. The sheet conveyance control unit 304 controls the conveyance of the sheet 110 by controlling the driving of the stepping motors 121, 123, and 125 based on the detection results of the first sensor 131 to the third sensor 133 recorded in the recording unit 303. I do.

The power supply voltage may change due to external factors regardless of the power supply voltage switching control by the power supply switching control unit 301. Therefore, the sensor level detection unit 302 determines whether the first sensor 131 to the third sensor 133 are malfunctioning due to an unintended change in the power supply voltage. The sensor level detection unit 302 determines any malfunction of the first sensor 131 to the third sensor 133 according to the detection status of the voltage generated by the termination unit 134 (hereinafter, referred to as “termination level”). .. For example, when the first sensor 131 to the third sensor 133 operate normally, the sensor level detection unit 302 causes the first sensor 131 to the third sensor 133 to repeatedly perform the detection operation without detecting the terminal level. When the terminal level is detected, the sensor level detection unit 302 determines that any of the first sensor 131 to the third sensor 133 is malfunctioning.

In addition, for example, the sensor level detection unit 302 compares the number of times the power supply switching controller 301 has switched the power supply voltage with the number of sensors connected in series, and determines from the verification result whether or not a malfunction has occurred. The number of times the power supply voltage is switched is the number of times the power supply voltage is switched to 5 [V] during the period from the initialization of each sensor to the detection of the termination level. The sensor level detection unit 302 can count the number of times of switching based on a switching signal output from the power supply switching control unit 301, for example. When the first sensor 131 to the third sensor 133 operate normally, the number of sensors connected in series and the number of times the power supply voltage is switched have a predetermined relationship. When any of the first sensor 131 to the third sensor 133 malfunctions, the number of sensors connected in series and the number of times the power supply voltage is switched are not in a predetermined relationship. The sensor level detection unit 302 can also determine the malfunction of the first sensor 131 to the third sensor 133 using such a principle.

In addition, as an external factor in which the power supply voltage changes unintentionally, static electricity or the like is directly applied to the wiring connecting the main substrate 200 and the first sensor 131 to the third sensor 133, or indirectly. Can be electrically induced. Such an external factor exerts an influence on the power supply voltage such that it crosses the threshold voltage (for example, 4 [V]) of the voltage detection units 211a to 211c, so that the power supply voltage is switched unintentionally and the sensor malfunctions. Occurs.

The recording unit 303 records the detection result of each sensor in a register or the like (not shown). When the sensor level detection unit 302 determines that a malfunction has occurred, the detection result recorded in the recording unit 303 is deleted. This is to prevent the sheet conveyance control based on the inappropriate sensor detection result due to the malfunction when the sensor malfunctions. By preventing the conveyance control of the sheet based on the detection result of the inappropriate sensor, the conveyance error such as the conveyance jam of the sheet 110 is prevented.

(Sensor operation control)
FIG. 4 is a flowchart showing an operation control process for controlling the sensor detection operation by the main board 200. In this process, the CPU 201 determines that any of the first sensor 131 to the third sensor 133 is malfunctioning when the terminal level is detected. 5 and 6 are timing charts at the time of operation control processing. The timing chart of FIG. 5 shows a case where each sensor operates normally. The timing chart of FIG. 6 shows a case where a malfunction occurs in any of the sensors.

First, an operation control process when each sensor operates normally will be described.
When the detection operation of the sensor is started, the CPU 201 sets the power supply voltage output by the power supply switching unit 202 to 0 [V], and initializes the switching number n at which the power supply switching unit 202 switches the power supply voltage to “0”. (S301). The number of switching times n in the present embodiment is the number of times the power supply voltage is switched to 5 [V]. The CPU 201 counts the number of switching times n, and adds 1 to the number of switching times n when the power supply voltage is set to 5 [V]. The CPU 201 waits for a predetermined time (100 microseconds in this embodiment) while keeping the power supply voltage at 0 [V] (S302). The predetermined time is set to a time sufficient to control the power shutoff units 212a, 212b, 212c to a shutoff state (state in which the power supply voltage is not supplied to the configuration after the second sensor 132).

When the power supply voltage is set to 0 [V] and a predetermined time elapses, the CPU 201 sets the power supply voltage output by the power supply switching unit 202 to 5 [V] (S303). Further, the CPU 201 increments the switching number n by 1 in accordance with the switching operation of the power supply voltage (S304). At this time, the voltage detection unit 211a is in the first state, and the LED control unit 215a causes the LED 213a to emit light. Since the power cutoff unit 212a is in the cutoff state, the power supply voltage is not supplied to the second sensor 132 and the third sensor 133. The number of switching times n becomes “1”. The CPU 201 waits for a predetermined time (100 microseconds in the present embodiment) with the power supply voltage set to 5 [V] (S305). The predetermined time is set to be longer than the time from when the power supply voltage is applied to the first sensor 131 until the detection result of the first sensor 131 is input to the CPU 201.

When the power supply voltage is 5 [V] and a predetermined time has elapsed, the CPU 201 acquires the voltage value of the signal line and confirms the detection result of the first sensor 131 (S306). In the process of S306, the CPU 201 detects, based on the voltage value, whether the phototransistor 214a of the first sensor 131 is in a conductive state in which light is received or in a cutoff state in which light is not received. The phototransistor 214b of the second sensor 132 and the phototransistor 214c of the third sensor 133 are also connected to the signal line connecting the phototransistor 214a and the CPU 201. However, since the power cutoff unit 212a of the first sensor 131 is in the cutoff state, the power supply voltage is not supplied to the second sensor 132 and the third sensor 133. As a result, while the CPU 201 acquires the detection result of the phototransistor 214a, the output value of the signal line changes based on only the detection result of the phototransistor 214a.

When the output value of the signal line is 0 [V], the CPU 201 determines that the phototransistor 214a of the first sensor 131 is conductive. That is, when the output value of the signal line is 0 [V], the first sensor 131 does not detect the sheet 110. When the output value of the signal line is 3.3 [V], the CPU 201 determines that the phototransistor 214a of the first sensor 131 is in the cutoff state. That is, when the output value of the signal line is 3.3 [V], the first sensor 131 detects the sheet 110. In this way, the CPU 201 can determine the detection state of the first sensor 131 by acquiring the output value of the signal line in the process of S306.
The processing of S303 to S306 is processing from time t11 to time t12 in FIG. In the example of FIG. 5, a waveform when the light of the LED 213a is received by the phototransistor 214a is shown. When there is a shield between the LED 213a and the phototransistor 214a, the phototransistor 214a is in the cutoff state and the output value of 3.3 [V] is detected.

After obtaining the detection result, the CPU 201 determines whether or not the sensor level detection unit 302 has detected the terminal level (S307). The termination level is a voltage value different from 0 [V] and 3.3 [V] depending on the driving state of the phototransistors 214a to 214c of each sensor. The termination level is a voltage value obtained by dividing the power supply voltage of 5 [V] by the termination resistors 216 and 217 of the termination unit 134, and is 2.5 [V], for example.

When the termination level is not detected (S307:N), the CPU 201 temporarily records the detection result in the recording unit 303 (S308). The CPU 201 determines whether the sensor that has obtained the detection result is connected to the most downstream side of the series connection (S309). The CPU 201 has, for example, a configuration of the sensors connected in series (the number, etc.) registered in advance, and determines from the configuration and the acquired number of switching times n whether the sensor that has obtained the detection result is connected to the most downstream side. To do.

When the sensor that has acquired the detection result is not the most downstream sensor (S309: N), the CPU 201 controls the power supply switching unit 202 to switch the power supply voltage from 5 [V] to 3.3 [V] (S310). .. At this time, the voltage detection unit 211a changes from the first state to the second state because the fall of the power supply voltage is detected. After that, the voltage detection unit 211a maintains the second state until the power supply voltage becomes 0 [V]. When the voltage detection unit 211a is in the second state, the power cutoff unit 212a is in the conductive state and is controlled to be able to supply the power supply voltage to the second sensor 132 provided downstream. The LED control unit 215a of the first sensor 131 enters a cutoff state and cuts off the current supply to the LED 213a. Therefore, the LED 213a of the first sensor 131 is turned off. That is, the phototransistor 214a is turned off.

The CPU 201 stands by for a predetermined time (75 microseconds in this embodiment) while setting the power supply voltage to 3.3 [V] (S311). The predetermined time may be the time required for the state of the voltage detection unit 211a of the first sensor 131 to change to the second state. The processing of S308 to S311 is processing from time t12 to time t13 in FIG. When the power cutoff unit 212a of the first sensor 131 is in the conductive state, the power supply voltage can be supplied to the second sensor 132. When the supply of the power supply voltage is started, the voltage detection unit 211b of the second sensor 132 is controlled to the first state. The power shutoff unit 212b of the second sensor 132 is controlled to be shut off. The LED control unit 215b of the second sensor 132 becomes conductive. The LED 213b emits light because current flows.

After the elapse of the predetermined time, the CPU 201 performs the processes of S303 to S306 again. As a result, the CPU 201 acquires the detection result of the second sensor 132. In the process of S304, the number of switching times n becomes "2". In the process of S307, the phototransistor 214a of the first sensor 131 and the phototransistor 214c of the third sensor 133 are controlled to be inactive. Therefore, the output value of the signal line changes only based on the detection result of the phototransistor 214b of the second sensor 132. The processing of S303 to S305 is processing from time t13 to time t14 in FIG.

After acquiring the detection result of the second sensor 132, the CPU 201 records the acquired detection result of the second sensor 132 in the recording unit 303 (S308) because the terminal level is not detected (S307:N). Since the second sensor 132 is not the most downstream sensor (S309:N), the CPU 201 switches the power supply voltage to 3.3 [V] and waits for a predetermined time (S310, S311). As a result, the voltage detection unit 211b of the third sensor 133 is controlled to the first state, and the LED 213c emits light.

After the elapse of the predetermined time, the CPU 201 performs the processes of S303 to S306 again. As a result, the CPU 201 acquires the detection result of the third sensor 133. In the process of S304, the switching number n becomes "3". In the process of S307, the phototransistor 214a of the first sensor 131 and the phototransistor 214b of the second sensor 132 are controlled to be inoperative. Therefore, the output value of the signal line changes based on only the detection result of the phototransistor 214c of the third sensor 133. The processing of S303 to S305 is processing from time t15 to time t16 in FIG. As described above, the CPU 201 can acquire a stable detection result by acquiring the detection result of the sensor at the timing before changing the power supply voltage from 5 [V] to 3.3 [V].

Since the CPU 201 has not detected the termination level after the detection result of the third sensor 133 is acquired (S307:N), the CPU 201 records the acquired detection result of the third sensor 133 in the recording unit 303 (S308). Since the switching number n is “3”, the CPU 201 determines that the third sensor 133 is the most downstream sensor (S309:Y), and recording of the detection results for the number of sensors is completed in the sheet conveyance control unit 304. Is notified (S313). Based on this notification, the sheet conveyance control unit 304 reads the detection result temporarily recorded in the recording unit 303, determines whether the sheet 110 is detected at the detection position within a predetermined timing, and controls the conveyance of the sheet 110. To do. The sheet conveyance control unit 304 deletes the read detection result from the recording unit 303.

The CPU 201, which has notified the sheet conveyance control unit 304 that the recording of the detection result has been completed, determines whether to end the process (S316). The CPU 201 determines the end of the process based on an instruction from the sheet conveyance control unit 304, based on whether or not the sheet conveyance control in the machine is continuously performed. When the process is not finished (S316: N), the CPU 201 returns to the process of S301, sets the power supply voltage to 0 [V], and resets the switching number n to "0". When the predetermined time elapses as it is (S302), the voltage detection units 211a, 211b, and 211c of the first sensor 131 to the third sensor 133 are in the first state. Therefore, the power shutoff units 212a, 212b, and 212c shift to a shutoff state (state in which the power supply voltage is not supplied to the second sensor 132 and the third sensor 133).

The CPU 201 repeats the processing of S301 to S311, S313, and S316 while the first sensor 131 to the third sensor 133 operate normally, and sequentially acquires the detection results of the first sensor 131 to the third sensor 133.
In the above processing, the first sensor 131 to the third sensor 133 perform the same operation with respect to the input signal (power supply voltage). However, by shifting the supply timing of the power supply voltage to each sensor, the CPU 201 can independently detect the states of all the sensors.

Next, the operation control process when any of the sensors malfunctions will be described with reference to FIG. Similar to the normal operation, the CPU 201 initializes the first sensor 131 to the third sensor 133 and acquires the detection result of the first sensor 131 (S301 to S306). The CPU 201 records the detection result of the first sensor 131 in the recording unit 303 (S308), and then operates to acquire the detection result of the second sensor 132 (S310, S311, S303 to S305).

At this time, in FIG. 6, the power supply voltage of 5 [V] applied to the second sensor 132 between the time t13 and the time t14 has noise enough to cause the sensor to malfunction. The voltage detection unit 211b of the second sensor 132 enters the second state when the power supply voltage fluctuates across the threshold voltage due to noise. As a result, the power cutoff unit 212b becomes conductive, and the power supply voltage is supplied to the third sensor 133. That is, due to the noise, the supply destination of the power supply voltage is switched from the second sensor 132 to the third sensor 133 regardless of the power supply voltage switching control by the power supply switching unit 202. Since the switching is performed before the detection result of the second sensor 132 is acquired, the CPU 201 acquires the detection result of the third sensor 133 in the process of S306 after the detection result of the first sensor 131 is acquired. As a result, the number of detection results to be acquired is smaller than the number of sensors connected in series, and the order of acquisition of detection results is inconsistent.

In the configuration of this embodiment, when the supply destination of the power supply voltage is switched before the detection result is acquired in this way, the power supply voltage is supplied to the termination unit 134 by continuing the processing. In the example of FIG. 6, the CPU 201 applies the power supply voltage of 5 [V] to the terminating unit 134 from the time t15 by performing the processes of S308 to S311 and S303 to S306 after acquiring the detection result of the third sensor 133. Will be done. Therefore, the CPU 201 acquires the voltage (termination level) generated by the resistance voltage division in the termination unit 134.

During normal operation shown in FIG. 5, the number of detection results to be acquired does not exceed the number of sensors connected in series, and the acquisition order of detection results is consistent. Therefore, the CPU 201 does not acquire the termination level generated by the termination unit 134, and determines that the detection result of the termination unit 134 has not been acquired in the process of S307 of FIG. However, if a malfunction of the sensor occurs and a mismatch occurs in the acquisition order of the detection results, the CPU 201 determines that the termination level generated by the termination unit 134 in the processing of S307 has been acquired. In this way, the CPU 201 can determine that any sensor has malfunctioned by acquiring the termination level generated by the termination unit 134.

From the above, the CPU 201 acquires the termination level generated by the termination unit 134 when any of the sensors malfunctions (S306), and determines that the sensor level detection unit 302 has detected the termination level (S307). : Y). In this case, the CPU 201 deletes (clears) all the detection results recorded in the recording unit 303 (S312). By clearing all the detection results, it is possible to prevent the sheet conveyance control unit 304 from performing the conveyance control of the sheet 110 based on the detection result obtained as a result of the malfunction of the sensor.

The CPU 201 confirms whether or not the number of times the terminal level is continuously acquired is a predetermined number (M times) (S314). The M number of times is the number of times set by the sheet conveyance control unit 304 from the minimum time interval that requires the detection result of each sensor during the conveyance control of the sheet 110. When the number of times the terminal level is continuously acquired becomes a certain number of times or more (M times or more), the CPU 201 determines that the detection result of the sensor necessary for the sheet conveyance control cannot be obtained and the sheet conveyance cannot be performed normally. .. Therefore, when the number of times the terminal level is continuously acquired reaches M times (S314:Y), the CPU 201 instructs the sheet conveyance control unit 304 to stop the sheet conveyance, and notifies the user of an error by a not-shown notifying unit. (S315). The notification unit notifies the error by, for example, displaying an error message on the display unit or a warning sound.

It should be noted that the CPU 201 determines the end of the process if the number of times the terminal level has been continuously acquired is less than M (S314: N) (S316). When not ending (S316:N), the CPU 201 repeats the processing from S301. When ending (S316: Y), the CPU 201 ends the operation control process.

In the configuration described above, the CPU 201 alternately supplies two types of power supply voltage (5 [V], 3.3 [V]) to the most upstream sensor (first sensor 131) of the plurality of sensors connected in series. Apply to. Each sensor performs a detection operation when one power supply voltage is applied, and supplies a power supply voltage to the sensor at the subsequent stage when the other power supply voltage is applied. When the other power supply voltage is applied and the power supply voltage is supplied to the subsequent sensor, each sensor maintains the supply operation state until the power supply voltage of 0 [V] is applied and initialized. .. Therefore, the CPU 201 alternately applies two types of power supply voltages, so that the plurality of sensors connected in series can perform the detection operation in time division in order from the most upstream sensor.

A terminating unit 134 is connected to the downstream of the most downstream sensor of the plurality of sensors connected in series. When each sensor operates normally, the CPU 201 can acquire the detection result in order from the most upstream sensor. In this case, each sensor is initialized after the power supply voltage is applied to the most downstream sensor of the plurality of sensors connected in series, and the power supply voltage is applied again in order from the most upstream sensor. Therefore, the power supply voltage is not applied to the termination unit 134.

However, when any of the sensors malfunctions, each sensor is not initialized after the power supply voltage is applied to the most downstream sensor of the plurality of sensors connected in series, and the power supply voltage is applied to the termination unit 134. When the power supply voltage is applied to the terminating unit 134, the CPU 201 acquires a voltage value (termination level) different from the voltage value acquired as the detection result of the sensor. By obtaining the different voltage values, the CPU 201 can confirm that the termination level has been obtained from the termination unit 134, and can determine that one of the sensors is malfunctioning. When the CPU 201 determines that the sensor has malfunctioned, it discards the sensor detection results acquired up to that point. Therefore, the influence of the malfunction on the control according to the detection result of the sensor, for example, the sheet conveyance control is prevented. In this way, the influence of noise generated on the power supply voltage is suppressed.

(Modification)
FIG. 7 is a flowchart showing another operation control process for controlling the detection operation of the sensor by the main board 200. In this process, the CPU 201 collates the number of times the power source switching controller 301 has switched the power source voltage with the number of sensors connected in series, and determines from the collation result whether or not a malfunction has occurred. 8 and 9 are timing charts at the time of operation control processing. The timing chart of FIG. 8 shows a case where each sensor operates normally. The timing chart of FIG. 9 shows a case where a malfunction occurs in any of the sensors.

The CPU 201 acquires the detection results of the first sensor 131 to the third sensor 133 and records them in the recording unit 303 by repeating the same processing as the processing of S301 to S311 in FIG. 4 (S401 to S411). After that, since the third sensor 133 is the most downstream sensor, the CPU 201 notifies the sheet conveyance control unit 304 that the recording of the detection results for the number of sensors is completed, as in the process of S313 in FIG. Yes (S413). Based on this notification, the sheet conveyance control unit 304 reads the detection result temporarily recorded in the recording unit 303, determines whether the sheet 110 is detected at the detection position within a predetermined timing, and controls the conveyance of the sheet 110. To do. The sheet conveyance control unit 304 deletes the read detection result from the recording unit 303.

The CPU 201 that has notified the detection result controls the power supply switching unit 202 to switch the power supply voltage from 5 [V] to 3.3 [V] (S410). At this time, the voltage detection unit 211c changes from the first state to the second state in order to detect the fall of the power supply voltage. After that, the voltage detection unit 211c maintains the second state until the power supply voltage becomes 0 [V]. When the voltage detection unit 211c is in the second state, the power cutoff unit 212c is in the conductive state, and the power supply voltage is controlled to be able to be supplied to the termination unit 134 provided in the subsequent stage. The LED control unit 215c of the third sensor 133 enters a cutoff state and cuts off the current supply to the LED 213c. Therefore, the LED 213c of the third sensor 133 is turned off. That is, the phototransistor 214c is turned off.

The CPU 201 waits for a predetermined time while setting the power supply voltage to 3.3 [V] (S411). The predetermined time may be the time required for the state of the voltage detection unit 211c of the third sensor 133 to change to the second state. The processing of S308 to S311 is processing from time t16 to time t17 in FIG. When the power cutoff part 212c of the third sensor 133 is turned on, the power supply voltage can be supplied to the termination unit 134. When the supply of the power supply voltage is started, the termination unit 134 generates a voltage value (termination level) obtained by resistively dividing the power supply voltage.

After the elapse of the predetermined time, the CPU 201 performs the processing of S403 to S406 again. As a result, the CPU 201 acquires the termination level. In the processing of S404, the number of switching times n becomes "4". In the process of S407, the phototransistors 214a, 214b, and 214c of the first sensor 131 to the third sensor 133 are controlled to be inoperative. Therefore, the output value of the signal line changes only based on the termination level. The processing of S403 to S405 is processing from time t17 to time t18 in FIG.

The CPU 201 that has detected the terminal level (S407: Y) clears all the detection results recorded in the recording unit 303 (S412). The CPU 201 detects the malfunction of the sensor by determining whether the switching number n is one more than the number N of the sensors connected in series (S414). When the sensor operates normally, the power supply voltage is set to 5 [V] once more than the number of sensors. Therefore, by comparing the number of switching times n with the number of sensors N, it is possible to detect a malfunction of the sensor.

However, the number of switching times n becomes equal to or less than the number N of sensors due to the malfunction of the sensor. In FIG. 9, the power supply voltage fluctuates between time t13 and time t14, so that the sensor that performs the detection operation is switched to the downstream sensor without the switching number n being incremented. That is, the third sensor 133 is performing the detection operation before the CPU 201 acquires the detection result of the second sensor 132. As a result, the number of switching times n becomes the same as the number N of sensors between the time when each sensor is reset in the processing of S401 and the time when the terminal level is acquired by the CPU 201. In this way, the CPU 201 can determine that one of the sensors has malfunctioned because the number of times of switching when the terminal level is acquired is less than or equal to the number of sensors.

When the sensor malfunctions (S414: Y), the CPU 201 instructs the sheet conveyance control unit 304 to stop the sheet conveyance, and notifies the user of the error by a not-shown notifying unit (S415). The notification unit notifies the error by, for example, displaying an error message on the display unit or a warning sound. If the sensor is not malfunctioning (S414:N), the CPU 201 determines the end of the process (S416), as in the process of S316 of FIG. When not ending (S416:N), the CPU 201 repeats the processing from S301. When ending (S416: Y), the CPU 201 ends the operation control process.

In this way, when the CPU 201 determines that the sensor has malfunctioned, it discards the sensor detection results acquired up to that point. Therefore, the influence of the malfunction on the control according to the detection result of the sensor, for example, the sheet conveyance control is prevented. In this way, the influence of noise generated on the power supply voltage is suppressed.

(Second embodiment)
The second embodiment is different from the first embodiment in the configuration of the main board and the sensor (configuration of the sensor control device), but the configuration of the image forming apparatus is the same. Description of the configuration of the image forming apparatus is omitted. FIG. 10 is a configuration diagram of a sensor control device including a main board and a sensor included in the controller of the present embodiment. The main board 600 is a sensor control device that controls the operations of the first sensor 701 to the third sensor 703 and acquires the detection results thereof. In the relationship with the image forming apparatus 100 in FIG. 1, the sensor 131 corresponds to the first sensor 701, the sensor 132 corresponds to the second sensor 702, and the sensor 133 corresponds to the third sensor 703. The termination unit 134 corresponds to the termination unit 704.

The first sensor 701 to the third sensor 703 are serially connected to the main board 600. The first sensor 701 to the third sensor 703 are connected in this order from the upstream side to the first sensor 701, the second sensor 702, and the third sensor 703 with the main board 600 side as the upstream side. The first sensor 701 to the third sensor 703 have the same internal configuration. The terminating unit 704 is connected to the subsequent stage of the third sensor 703 provided on the most downstream side.

The main board 600 and the first sensor 701, the first sensor 701 and the second sensor 702, the second sensor 702 and the third sensor 703, and the third sensor 703 and the termination unit 704 are connected by different power supply lines. A power supply voltage is applied from the main board 600 to the first to third sensors 701 to 703 and the termination unit 704 by the power supply line. The detection results of the first sensor 701 to the third sensor 703 and the voltage (termination level) generated by the termination unit 704 are input to the main board 600 by the power supply line. The main board 600, the first sensor 701, the second sensor 702, the third sensor 703, and the termination unit 704 are commonly grounded.

The main board 600 includes a CPU 601 that controls at least the operations of the first sensor 701 to the third sensor 703, and a power supply switching unit 602 that switches the power supply voltage applied to the first sensor 701 to the third sensor 703 and the termination unit 704. Equipped with. The power supply switching unit 602 applies power supply voltages of three different voltage values to the first sensor 701 to the third sensor 703 and the termination unit 704. In the present embodiment, the power supply switching unit 602 uses three types of power supply voltage to be applied to the first sensor 701 to the third sensor 703 and the termination unit 704: 0 [V], 3.3 [V], and 5 [V]. Switch. The power supply switching unit 602 includes two switch units 604 and 605. When the switch unit 604 is in the conductive state and the switch unit 605 is in the cut-off state, the power supply voltage is 5 [V]. When the switch unit 604 is in the cutoff state and the switch unit 605 is in the conductive state, the power supply voltage is 3.3 [V]. When both the switch units 604 and 605 are in the cutoff state, the power supply voltage becomes 0 [V]. The main board 600 includes a pull-up resistor 606 in the power supply switching unit 602 for acquiring the detection results of the first sensor 701 to the third sensor 703 and the voltage generated in the termination unit 704. A predetermined voltage (here, 3.3 [V]) is applied to one end of the pull-up resistor 606 via the switch unit 605. The main board 600 includes a connector 603 for connecting to the first sensor 701 via a power supply line. The CPU 601 realizes the functions shown in FIG.

The first sensor 701 includes a connector 610a, a voltage detection unit 611a, a power cutoff unit 612a, an LED 613a, a phototransistor 614a, an LED control unit 615a, and a sensor latch unit 616a. The first sensor 701 has a configuration in which a sensor latch unit 616a is added to the first sensor 131 of FIG. The same applies to the second sensor 702 and the third sensor 703. The difference between each part and the configuration of FIG. 2 will be described.

The collector terminal of the phototransistor 614a is connected to the sensor latch portion 616a. When the phototransistor 614a is in the conductive state, the ground voltage (0 [V]) is input to the sensor latch unit 616a as the detection result of the first sensor 701. When the phototransistor 614a is in the cutoff state, the power supply voltage is input to the sensor latch unit 616a as the detection result of the first sensor 701. The sensor latch unit 616a can latch the conductive state and the cutoff state (open state) of the phototransistor 614a.

Therefore, the sensor latch unit 616a includes a transistor 617a that functions as a switch element and a resistor 618a. In the sensor latch portion 616a, the transistor 617a changes to a conductive state or a cutoff state (open state) depending on the state of the voltage detection portion 611a and the operation of the phototransistor 614a. The collector terminal of the transistor 617a is connected to the power supply line of the first sensor 701 at the contact a through the resistor 618a. The power supply line to which the contact a is connected is connected to the A/D port of the CPU 601. With such a configuration, the CPU 601 can detect the conductive state and the cutoff state (open state) of the transistor 617a.

The connector 610a is connected to the main substrate 600 via a power supply line, and is also connected to the second sensor 702 provided on the downstream side via another power supply line. Unlike the first embodiment, the signal line is not connected to the connector 610a.

The voltage detection unit 611a detects the rising and falling of the power supply voltage applied from the main substrate 600, for example, with the threshold value set to 4 [V]. However, the voltage detection unit 611a does not detect the rise when the voltage is changed from 0 [V] to 4 [V] or more when the power is turned on. The voltage detection unit 611a is in the “first state” after the power supply voltage is turned on. The voltage detection unit 611a maintains the first state until the applied power supply voltage once exceeds 4 [V] (for example, 5 [V]) and then detects a falling edge that crosses 4 [V]. When the falling of the applied power supply voltage over 4 [V] is detected, the voltage detection unit 611a is in the “second state”. After that, when the rise of the applied power supply voltage over 4 [V] is detected, the voltage detection unit 611a enters the “third state”. The voltage detection unit 611a in the third state maintains the third state until the power supply voltage becomes 0 [V]. The change of the power supply voltage to 0 [V] is called “initialization”.

When the voltage detection unit 611a is in the first state, the power cutoff unit 612a is in the cutoff state and does not supply the power supply voltage to the second sensor 702 located downstream. The power shutoff unit 612a is also in the shutoff state when the voltage detection unit 611a is in the second state. The power cutoff unit 612a is in a conductive state in which the power supply voltage is supplied to the second sensor 702 located downstream when the voltage detection unit 611a is in the third state.

When the voltage detection unit 611a is in the first state, the LED control unit 615a is in a conductive state and supplies a current to the LED 613a to emit light. When the voltage detection unit 611a is in the second state, the LED control unit 615a enters the cutoff state to cut off the current to the LED 613a and turn off the light. After that, the LED control unit 615a maintains the cutoff state until the power supply voltage changes to 0 [V] (initialization) even if the voltage detection unit 611a enters the third state.

The sensor latch unit 616a turns off the transistor 617a when the voltage detection unit 611a is in the first state. When the voltage detection unit 611a switches from the first state to the second state, the sensor latch unit 616a latches the state signal (detection result) from the phototransistor 614a and operates the transistor 617a according to the latched result.
The sensor latch unit 616a holds the transistor 617a in a conductive state if the phototransistor 614a is in a conductive state (input is 0 [V]) when the voltage detection unit 611a is switched from the first state to the second state. If the phototransistor 614a is in the cutoff state (input is the power supply voltage level), the sensor latch unit 616a holds the transistor 617a in the cutoff state. After that, the sensor latch unit 616a turns off the transistor 617a when the voltage detection unit 611a switches to the third state. The sensor latch unit 616a maintains this state until the power supply voltage changes (initializes) to 0 [V]. In this way, the sensor latch unit 616a can hold the light receiving state of the phototransistor 614a. The CPU 601 can acquire the detection result of the first sensor 701 by detecting the conduction state and the cutoff state of the transistor 617a.

The connector 610b of the second sensor 702 is connected to the upstream first sensor 701 via a power supply line, and is also connected to the downstream third sensor 703 via another power supply line. The signal line as in the first embodiment is not connected to the connector 610b. The second sensor 702 includes a voltage detection unit 611b, a power cutoff unit 612b, an LED 613b, a phototransistor 614b, an LED control unit 615b, and a sensor latch unit 616b. The operation of each unit is the same as the operation of each unit of the corresponding first sensor 701, and thus the description thereof will be omitted.

The collector terminal of the transistor 617b in the sensor latch unit 616b is connected to the contact b of the power supply line of the second sensor 702 via the resistor 618b. The contact b is connected to the A/D port of the CPU 601 of the main board 600 via the first sensor 701. With such a configuration, the CPU 601 can detect whether the transistor 617b is on or off as a detection result of the second sensor 702.

The connector 610c of the third sensor 703 is connected to the second sensor 702 on the upstream side via a power supply line, and is also connected to the termination unit 704 provided on the downstream side via another power supply line. The signal line as in the first embodiment is not connected to the connector 610c. The third sensor 703 includes a voltage detection unit 611c, a power cutoff unit 612c, an LED 613c, a phototransistor 614c, an LED control unit 615c, and a sensor latch unit 616c. The operation of each unit is the same as the operation of each unit of the corresponding first sensor 701, and thus the description thereof will be omitted.

The collector terminal of the transistor 617c in the sensor latch unit 616c is connected to the contact c of the power supply line of the third sensor 703 via the resistor 618c. The contact point c is connected to the A/D port of the CPU 601 of the main board 600 via the first sensor 701 and the second sensor 702. With such a configuration, the CPU 601 can detect the conduction state and the cutoff state of the transistor 617c as the detection result of the third sensor 703.

Unlike the configuration of the first sensor 701 to the third sensor 703, the termination unit 704 includes a resistance element for resistively dividing the power supply voltage supplied from the power cutoff unit 612c of the third sensor 703. The termination unit 704 of this embodiment includes a termination resistor 620 as such a resistance element. The termination unit 704 generates a voltage (termination level) obtained by resistance-dividing the power supply voltage by the pull-up resistor 606 and the termination resistor 620 of the main board 600. The voltage value of the resistance-divided power supply voltage is connected to the power supply line of the third sensor 703 at the contact c of the third sensor 703. Therefore, the output value of the power supply line connecting the first sensor 701 and the main board 600 may be a voltage value divided by resistance. Further, the terminating resistor 620 is set such that the voltage value generated by the resistance voltage division by the pull-up resistor 606 and the terminating resistor 620 is different from the voltage value of the detection result of the first sensor 701 to the third sensor 703. The resistance value of is set. Therefore, the CPU 601 can identify whether the voltage value acquired via the power supply line is the detection result of the first sensor 701 to the third sensor 703 or the voltage value of the voltage generated by the terminal unit 704. Has become.

With the above configuration, the first sensor 701 to the third sensor 703 perform the same operation with respect to the input signal (power supply voltage). The main substrate 600 can sequentially apply the two types of power supply voltages (5 [V] and 3.3 [V]) to the plurality of sensors to cause the sensors to sequentially perform the detection operation. The main substrate 600 sequentially switches and applies the power supply voltage of each voltage value regardless of, for example, the conveyance timing of the sheet 110.

The main board 600 resets the state of each sensor by applying another power supply voltage (0 [V]), and causes the first-stage sensor (first sensor 701) to perform the detection operation again sequentially. Each sensor can have the same interface for connecting to the main substrate 600 or another sensor regardless of the connection location (upstream, downstream, or midway) in the serial connection. Therefore, it is possible to use the same sensor (same external shape, same internal circuit) for all the sensors. Each sensor does not require connection management between the sensor and the sensor or change the outer shape of each sensor, and has an inexpensive configuration that does not require a complicated control circuit such as packet communication. In this embodiment, three sensors are connected in series, but the number of sensors can be further increased by the same control.

By connecting the power supply lines in this manner, the number of power supply lines connecting the main substrate 600 and the plurality of sensors (first sensor 701 to third sensor 703) can be suppressed. Therefore, it becomes possible to reduce the number of cables and the number of connectors, and to suppress the cost and the component management cost. Further, it is possible to reduce the number of pins and the occupied area of the connector 603 of the main board 600 and reduce the cost.

(Sensor operation control)
FIG. 11 is a flowchart showing an operation control process for controlling the sensor detection operation by the main board 600. In this processing, the CPU 601 determines that any of the first sensor 131 to the third sensor 133 is malfunctioning when the terminal level is detected. 12 and 14 are timing charts at the time of operation control processing of the main board 600 and the first sensor 701. 13 and 15 are timing charts at the time of operation control processing. The timing charts of FIGS. 12 and 13 show the case where each sensor operates normally. The timing charts of FIGS. 14 and 15 show the case where a malfunction occurs in any of the sensors.

First, an operation control process when each sensor operates normally will be described.
The processing of S701 to S703 is the same as the processing of S301 to S303 in FIG. As a result, each sensor is initialized, the switching number n is initialized to "0", and the power supply voltage is set to 5 [V]. The CPU 601 counts the number of switching times n, and adds 1 to the number of switching times n when the power supply voltage is set to 5 [V]. The voltage detection unit 611a is in the first state, and the LED control unit 615a causes the LED 613a to emit light. Since the power cutoff unit 612a is in the cutoff state, the power supply voltage is not supplied to the second sensor 702 and the third sensor 703. The CPU 601 holds the power supply voltage (5 [V]) set in the process of S703 for a predetermined time and stands by (S704). The predetermined time is a time during which the LED 613a emits light and the light receiving operation of the phototransistor 614a is reliably performed.

After the elapse of a predetermined time, the CPU 601 sets the power supply voltage by the power supply switching unit 602 to 3.3 [V] pulled up by the pull-up resistor 606 (S705). As a result, the voltage detection unit 611a enters the second state by detecting the fall of the power supply voltage. When the voltage detection unit 611a enters the second state, the sensor latch unit 616a latches the state (detection result) of the phototransistor 614a and switches the operation state of the transistor 617a. The sensor latch unit 616a turns on the transistor 617a when the phototransistor 614a is in the conducting state, and turns off the transistor 617a when the phototransistor 614a is in the shutoff state.

When the voltage detection unit 611a is in the second state, the LED control unit 615a is in the cutoff state and the LED 613a is turned off. Since the LED 613a is turned off, the phototransistor 614a is turned off. At this time, if the extinguishing operation of the LED 613a is completed earlier than the latching operation of the sensor latch unit 616a, the sensor latch unit 616a may not be able to latch the state of the phototransistor 614a when the LED 613a is originally to be acquired. is there. Therefore, the voltage detection unit 611a delays the transmission of the control signal to the LED control unit 615a as compared with the transmission of the switching signal to the sensor latch unit 616a. The processing of S703 to S705 is processing from time t21 to time t22 in FIGS. 12 and 13.

The CPU 601 waits for a predetermined time (75 microseconds in the present embodiment) while keeping the power supply voltage at 3.3 [V] (S706). The predetermined time is longer than the state switching time of the voltage detection unit 611a and the sensor latch unit 616a. When the power supply voltage is 3.3 [V] and a predetermined time has elapsed, the CPU 601 acquires the voltage value of the power supply line to which the contact a in the first sensor 701 is connected and confirms the detection result of the first sensor 701. (S707). Accordingly, the CPU 601 detects whether the transistor 617a is in an operating state or a non-operating state (open). The processing of S706 and S707 is processing from time t22 to time t23 in FIGS.

The power supply line connecting the contact a in the first sensor 701 and the CPU 601 is also connected to the power supply lines from the second sensor 702, the third sensor 703, and the termination unit 704. However, since the power cutoff unit 612a of the first sensor 701 is in the cutoff state, the power supply voltage is not supplied to the device downstream of the second sensor 702. Further, although the voltage detection unit 611a and the LED control unit 615a are connected to the contact a in the first sensor 701, the current consumed by the lighting control of the voltage detection unit 611a and the LED 613a is small, and the current also flows to the LED 613a. The consumption current is very small because it does not exist. Therefore, at the time of the processing of S707, the transistor 617a when the power supply line operates is dominant. Therefore, the voltage value of the contact a (power supply line) connected to the A/D port of the CPU 601 is substantially determined by the state of the transistor 617a.

When the transistor 617a is in the conductive state, the voltage value acquired by the CPU 601 is determined by the voltage division ratio of the pull-up resistor 606 and the resistor 618a. In the present embodiment, the pull-up resistor 606 is set to 1.1 [kΩ] and the resistor 618a is set to 2.2 [kΩ], and the CPU 601 detects approximately 2.2 [V] (first in FIGS. 12 and 13). Sensor detection). When the transistor 617a is in the cutoff state, no current flows in the transistor 617a and almost no current flows in the power supply line, so the CPU 601 detects approximately 3.3 [V] (second sensor detection in FIG. 13).

The CPU 601 compares the A/D conversion result of the voltage value acquired at the A/D port with a predetermined threshold value and determines whether the transistor 617a is in the conductive state. In this embodiment, the threshold is 2.75 [V]. If the A/D conversion result is less than 2.75 [V], the CPU 601 determines that the transistor 617a is conductive and the first sensor 701 does not detect the sheet 110. If the A/D conversion result is 2.75 [V] or more, the CPU 601 determines that the transistor 617a is in the cutoff state and the first sensor 701 is detecting the sheet 110.

12 and 13 show waveforms when the light of the LED 613a is received by the phototransistor 614a, for the sake of explanation. Since there is no shield between the LED 613a and the phototransistor 614a, the phototransistor 614a receives light and becomes conductive. When the phototransistor 614a becomes conductive, the transistor 617a in the sensor latch portion 616a also becomes conductive. In this case, the voltage value acquired by the CPU 601 is 2.2 [V]. When there is a shield between the LED 613a and the phototransistor 614a, the phototransistor 614a does not receive light and enters a cutoff state (high impedance). Since the phototransistor 614a is turned off, the transistor 617a in the sensor latch unit 616a is also turned off (high impedance). In this case, the voltage value acquired by the CPU 601 is 3.3 [V].

The CPU 601 which has confirmed the detection result increments the switching number n by 1 (S708). The number of switching times n becomes “1” at this point. The CPU 601 determines whether or not the sensor level detection unit 302 has detected the terminal level (S709). The termination level is a voltage value different from 3.3 [V] and 2.2 [V] which are the detection results of the transistors 617a to 617c of each sensor. The termination level is a voltage value obtained by resistance-dividing the power supply voltage by the termination resistor 620 and the pull-up resistor 606. In the present embodiment, the termination level has a voltage value of 1.65 [V] when the termination resistance 620 is 1.1 [kΩ]. The determination threshold value for detecting the terminal level is 2.0 [V], for example. If the acquired detection result is equal to or less than the determination threshold value (2.0 [V] or less), the CPU 601 determines that the detection result is the terminal level.

When the termination level is not detected (S709:N), the CPU 601 temporarily records the detection result in the recording unit 303 (S711). The CPU 601 determines whether the sensor that has acquired the detection result is connected to the most downstream side of the series connection (S712). The CPU 601 registers, for example, the configuration (number, etc.) of sensors connected in series in advance, and determines from the configuration and the acquired number of switching times n whether the sensor that has obtained the detection result is connected to the most downstream side. To do.

When the sensor that has acquired the detection result is not the most downstream sensor (S712: N), the CPU 601 returns to the processing of S703 and controls the power supply switching unit 602 to switch the power supply voltage to 5 [V]. At this time, the voltage detection unit 611a of the first sensor 701 changes to the third state. Therefore, the sensor latch unit 616a turns off the transistor 617a. The power cutoff unit 612a becomes conductive, and the power supply voltage is supplied to the downstream second sensor 702.

Similar to the case of the first sensor 701, the CPU 601 acquires the detection result of the second sensor 502 (S704 to S707). In the process of S707, the transistor 617a of the first sensor 501 is in the cutoff state, and the third sensor 503 is not operating. Therefore, the input signal to the A/D port of the CPU 601 changes only based on the state of the transistor 617b of the second sensor 502. After acquiring the detection result of the second sensor 702, the CPU 601 increments the switching number n by 1 (S708). The number of switching times n becomes “2” at this point. The processing of S703 to S708 is processing from time t23 to time t25 in FIGS. 12 and 13. In FIG. 12 and FIG. 13, there is a shield between the LED 613b of the second sensor 702 and the phototransistor 614b, and the phototransistor 614b does not receive light and enters a cutoff state (high impedance). In this case, the voltage value acquired by the CPU 601 is 3.3 [V].

The CPU 601 determines whether or not the sensor level detection unit 302 has detected the terminal level (S709). Since the terminal level is not detected (S709:N), the CPU 601 records the acquired detection result of the second sensor 702 in the recording unit 303 (S711). Since the second sensor 702 is not the most downstream sensor (S712:N), the CPU 601 repeats the processing from S703 again. When repeating the processing from S703 onward, the CPU 601 sets the power supply voltage output by the power supply switching unit 602 to 5 [V] (S703). At this time, the voltage detection unit 611b of the second sensor 702 changes to the third state. Therefore, the sensor latch unit 616b turns off the transistor 617b. The power cutoff unit 612b becomes conductive, and the power supply voltage is supplied to the downstream third sensor 703.

Similar to the case of the first sensor 701 and the second sensor 702, the CPU 601 acquires the detection result of the third sensor 703 (S704 to S707). In the process of S707, the transistor 617a of the first sensor 701 and the transistor 617b of the second sensor 702 are in the cutoff state. Therefore, the input signal to the A/D port of the CPU 601 changes only based on the state of the transistor 617c of the third sensor 703. After acquiring the detection result of the third sensor 703, the CPU 601 increments the switching count n by 1 (S708). The switching number n becomes “3” at this point. The processing of S703 to S708 is processing from time t25 to time t27 in FIGS. 12 and 13. In FIGS. 12 and 13, there is no shield between the LED 613c of the third sensor 703 and the phototransistor 614c, and the phototransistor 614c receives light and becomes conductive. In this case, the voltage value acquired by the CPU 601 is 2.2 [V].

After acquiring the detection result of the third sensor 703, the CPU 601 records the acquired detection result of the third sensor 703 in the recording unit 303 because the terminal level is not detected (S709: N) (S711). The CPU 601 determines that the third sensor 133 is the most downstream sensor because the switching number n is “3” (S712:Y), and the recording of the detection results for the number of sensors is completed in the sheet conveyance control unit 304. The fact that it has done is notified (S713). Based on this notification, the sheet conveyance control unit 304 reads the detection result temporarily recorded in the recording unit 303, determines whether the sheet 110 is detected at the detection position within a predetermined timing, and controls the conveyance of the sheet 110. To do. The sheet conveyance control unit 304 deletes the read detection result from the recording unit 303. The CPU 601 that has notified the sheet conveyance control unit 304 that the recording of the detection result has been completed determines whether or not to end the process, similarly to the process of S316 in FIG. 4 (S715).

The CPU 601 repeatedly performs the processing of S701 to S709, S711 to 713, and S715 while the first sensor 701 to the third sensor 703 operate normally, and sequentially acquires the detection results of the first sensor 701 to the third sensor 703. ..
In the above processing, the first sensor 701 to the third sensor 703 perform the same operation with respect to the input signal (power supply voltage). However, by shifting the supply timing of the power supply voltage to each sensor, the CPU 601 can independently detect the states of all the sensors.

Next, an operation control process when any one of the sensors malfunctions will be described with reference to FIGS. 14 and 15. Similar to the normal operation, the CPU 601 initializes the first sensor 701 to the third sensor 703 and acquires the detection result of the first sensor 701 (S701 to S707).

At this time, in FIGS. 14 and 15, noise is generated in the power supply voltage of 5 [V] applied to the first sensor 701 between time t21 and time t22. In this case, the voltage detection unit 211a of the first sensor 701 changes from the first state to the second state and the third state as the power supply voltage fluctuates across the threshold voltage due to noise. As a result, the LED control unit 615a is turned off and the LED 613a is turned off. The sensor latch unit 616a latches the detection result from the phototransistor 614a, and operates the transistor 617a according to the latched result.

Further, when the voltage detection unit 211a is in the third state, the power cutoff unit 212a is in the conductive state and the power supply voltage is supplied to the second sensor 702. In other words, due to the noise, the supply destination of the power supply voltage is switched from the first sensor 701 to the second sensor 702 regardless of the power supply voltage switching control by the power supply switching unit 602. Since the CPU 601 performs the switching before the detection result of the first sensor 701 is acquired, the CPU 601 does not acquire the detection result of the first sensor 701 and the detection result of the second sensor 702 before the time t23 in the process of S707. Will be obtained. As a result, the number of detection results to be acquired is smaller than the number of sensors connected in series, and the order of acquisition of detection results is inconsistent.

In the configuration of this embodiment, when the supply destination of the power supply voltage is switched before the detection result is acquired in this way, the power supply voltage is supplied to the termination unit 704 by continuing the processing. In the example of FIGS. 14 and 15, the CPU 601 applies the power supply voltage of 5 [V] to the termination unit 704 from time t25 by performing the processing of S703 to S708 after acquiring the detection result of the third sensor 703. It will be. Therefore, the CPU 601 acquires the voltage value (termination level) generated by the resistance voltage division in the termination unit 704.

During normal operation as shown in FIGS. 12 and 13, the number of detection results to be acquired does not exceed the number of sensors connected in series, and the detection results are acquired in the same order. Therefore, the CPU 601 does not acquire the termination level generated by the termination unit 704, and determines that the detection result of the termination unit 704 has not been acquired in the process of S709 of FIG. However, if a malfunction of the sensor occurs and a mismatch occurs in the acquisition order of the detection results, the CPU 601 determines that the termination level generated by the termination unit 704 has been acquired in the processing of S709. In this way, the CPU 601 can determine that any sensor has malfunctioned by acquiring the termination level generated by the termination unit 704.

From the above, the CPU 601 acquires the termination level generated by the termination unit 704 when the sensor malfunctions (S707), and determines that the sensor level detection unit 302 has detected the termination level (S709:Y). .. After that, the CPU 601 clears all the detection results recorded in the recording unit 303, and notifies an error if the number of detections of the terminal level is M times, as in S312, S314, and S315 of FIG. 4 (S710, S714, S716). If the number of times the end level is detected is not M, the CPU 601 performs the processing from S715.

In the above configuration, the CPU 601 alternately supplies two kinds of power supply voltage (5 [V], 3.3 [V]) to the most upstream sensor (first sensor 701) of the plurality of sensors connected in series. Apply to. Each sensor performs a detection operation, a latch operation, and an operation of supplying the power supply voltage to the sensor in the subsequent stage according to the voltage value of the applied power supply voltage. When each sensor performs the operation of supplying the power supply voltage to the sensor in the subsequent stage, the sensor maintains the supply operation state until the initial state in which the power supply voltage of 0 [V] is applied. Therefore, the CPU 601 alternately applies two types of power supply voltages, so that the plurality of sensors connected in series can perform the detection operation in time division order from the most upstream sensor.

The termination unit 704 is connected to the downstream side of the most downstream sensor of the plurality of sensors connected in series. When each sensor operates normally, the CPU 601 can obtain the detection result in order from the most upstream sensor. In this case, each sensor is initialized after the power supply voltage is applied to the most downstream sensor of the plurality of sensors connected in series, and the power supply voltage is applied again in order from the most upstream sensor. Therefore, the power supply voltage is not applied to the termination unit 704.

However, if any of the sensors malfunctions, each sensor is not initialized after the power supply voltage is applied to the most downstream sensor of the plurality of sensors connected in series, and the power supply voltage is applied to the termination unit 704. When the power supply voltage is applied to the termination unit 704, the CPU 601 acquires a voltage value (termination level) different from the voltage value acquired as the detection result of the sensor. By acquiring the different voltage value, the CPU 601 can confirm that the voltage value is acquired from the termination unit 704, and can determine that one of the sensors is malfunctioning. When the CPU 601 determines that the sensor has malfunctioned, it discards the sensor detection results acquired up to that point. Therefore, the influence of the malfunction on the control according to the detection result of the sensor, for example, the sheet conveyance control is prevented. In this way, the influence of noise generated on the power supply voltage is suppressed.

(Modification)
FIG. 16 is a flowchart showing another operation control process for controlling the sensor detection operation by the main board 600. In this processing, the CPU 601 collates the number of times the power source voltage is switched by the power source switching unit 602 with the number of sensors connected in series, and determines from the collation result whether or not a malfunction has occurred. 17 and 18 are timing charts at the time of operation control processing. The timing chart of FIG. 17 shows a case where each sensor operates normally. The timing chart of FIG. 18 shows a case where a malfunction occurs in any of the sensors.

The CPU 601 acquires the detection results of the first sensor 701 to the third sensor 703 and records them in the recording unit 303 by repeating the same processing as the processing of S701 to S709, S711, and S712 of FIG. 11 (S801 to S809). , S811, S812). After that, since the third sensor 703 is the most downstream sensor, the CPU 601 notifies the sheet conveyance control unit 304 that the recording of the detection results for the number of sensors is completed, as in the process of S713 of FIG. Yes (S813). Based on this notification, the sheet conveyance control unit 304 reads the detection result temporarily recorded in the recording unit 303, determines whether the sheet 110 is detected at the detection position within a predetermined timing, and controls the conveyance of the sheet 110. To do. The sheet conveyance control unit 304 deletes the read detection result from the recording unit 303.

The CPU 601 that has notified the detection result performs the processing of S803 to S807 again. The processing of S803 to S807 is processing from time t28 to time t29 in FIG. When the power cutoff unit 612c of the third sensor 703 is turned on, the power supply voltage can be supplied to the terminal unit 704. When the supply of the power supply voltage is started, the termination unit 704 generates a voltage value (termination level) obtained by resistance-dividing the power supply voltage. In the process of S807, the CPU 601 acquires the termination level. The CPU 601 increments the switching number n by 1 (S808). As a result, the number of switching times n becomes "4".

The CPU 601 that has detected the terminal level (S809:Y) clears all the detection results recorded in the recording unit 303 (S810). The CPU 201 detects the malfunction of the sensor by determining whether the switching number n is one more than the number N of the sensors connected in series (S814). When the sensor operates normally, the power supply voltage is set to 5 [V] once more than the number of sensors. Therefore, by comparing the number of switching times n with the number of sensors N, it is possible to detect a malfunction of the sensor.

However, the number of switching times n becomes equal to or less than the number N of sensors due to the malfunction of the sensor. In FIG. 18, the power supply voltage fluctuates between time t21 and time t22, so that the sensor that performs the detection operation is switched to the downstream sensor without the switching number n being incremented. That is, the second sensor 702 performs the detection operation before the CPU 601 acquires the detection result of the first sensor 701. As a result, the number of switching times n becomes the same as the number N of sensors between the time when each sensor is reset in the processing of S801 and the time when the terminal level is acquired by the CPU 601. In this way, the CPU 201 can determine that one of the sensors has malfunctioned because the number of times of switching when the terminal level is acquired is less than or equal to the number of sensors.

When the sensor malfunctions (S814: Y), the CPU 601 instructs the sheet conveyance control unit 304 to stop the sheet conveyance, and notifies the user of an error by a not-shown notifying unit (S816). The notification unit notifies the error by, for example, displaying an error message on the display unit or a warning sound. When the sensor is not malfunctioning (S814:N), the CPU 601 determines the end of the process (S815), similarly to the process of S715 of FIG. When not ending (S815: N), the CPU 601 repeats the processing from S801. When ending (S815: Y), the CPU 601 ends the operation control process.

In this way, when the CPU 601 determines that the sensor has malfunctioned, it discards the sensor detection results acquired up to that point. Therefore, the influence of the malfunction on the control according to the detection result of the sensor, for example, the sheet conveyance control is prevented. In this way, the influence of noise generated on the power supply voltage is suppressed.

As described above, the image forming apparatus 100 of each embodiment includes the sensor control device having a configuration in which a plurality of sensors and the control board (main board 200) are connected in series. The sensor control device includes a termination unit after the most downstream sensor. Each sensor performs a detection operation and a power supply voltage supply operation to a subsequent stage according to the voltage values of the two types of power supply voltages supplied from the control board. The control board supplies the sensor while switching the power supply voltage to sequentially perform the detection operation from the upstream sensor and acquire the detection result. By obtaining the voltage value (termination level) generated by the termination unit, the control board can determine the malfunction of the sensor due to the noise generated in the power supply voltage. When the sensor malfunctions, the control board discards the detection result of the sensor, so that the malfunction of the control process using the detection result can be prevented.

Claims (16)

The control means includes a plurality of sensors connected in series to the control means, and a terminating means connected upstream of the control means and downstream of the most downstream sensor of the plurality of sensors. ,
Each of the plurality of sensors performs a detection operation when a first voltage is applied from the control unit, and a second voltage different from the first voltage is applied after the first voltage is applied from the control unit. When applied, the voltage applied from the control means is supplied to the sensor or the terminating means connected to the subsequent stage,
The termination means generates a termination level that is a voltage value different from the detection results of the plurality of sensors,
By repeatedly applying the first voltage and the second voltage, the control unit sequentially performs the detection operation from the upstream sensor and sequentially acquires the detection result of each sensor, and detects the termination level of the termination level. Based on, it is characterized by determining the malfunction of the sensor,
Sensor control device. The control unit determines that the plurality of sensors are operating normally when acquiring the detection results of each sensor in order, and one of the sensors malfunctions when acquiring the terminal level. It is characterized by determining that,
The sensor control device according to claim 1. The control means has a recording means for recording the detection results of the plurality of sensors, and when the terminal level is detected, the detection result recorded in the recording means is deleted.
The sensor control device according to claim 1. The control means may notify an error by a predetermined notification means when the number of times the terminal level is continuously acquired is a predetermined number.
The sensor control device according to claim 1. Each of the plurality of sensors is initialized when a third voltage different from the first voltage and the second voltage is applied from the control means to a sensor connected to a subsequent stage or the termination means. Shutting off the supply of voltage applied from the control means,
The control means repeatedly applies the first voltage and the second voltage after applying the third voltage, thereby sequentially performing the detection operation from the sensor on the upstream side and sequentially obtaining the detection result of each sensor. Then, the termination level is obtained after obtaining the detection result of the most downstream sensor, and the malfunction of the sensor is determined based on the number of times of switching to the first voltage and the number of the plurality of sensors. And
The sensor control device according to claim 1. The control unit determines that the sensor is not malfunctioning if the number of times of switching is one more than the number of the plurality of sensors, and if the number of switching is less than or equal to the number of the plurality of sensors, any one Is determined to be malfunctioning,
The sensor control device according to claim 5. The control means counts the number of times of switching, and when initializing each of the plurality of sensors, the number of times of switching is also initialized.
The sensor control device according to claim 5 or 6. The control means has a recording means for recording the detection results of the plurality of sensors, and when the terminal level is detected, the detection result recorded in the recording means is deleted.
The sensor control device according to claim 5. The control means, when determining that one of the sensors is malfunctioning, notifies the error by a predetermined notification means,
The sensor control device according to claim 5. The terminating means comprises a terminating resistor for resistively dividing the voltage supplied from the control means to generate a terminating level.
The sensor control device according to claim 1. Each of the plurality of sensors is
A detection unit that performs a detection operation according to the first voltage;
First switch means provided in a voltage application path from the control means to the detection means,
Second switch means provided in a supply path for supplying the voltage applied from the control means to the sensor connected to the subsequent stage or the terminal means,
When the voltage of the applied path is the first voltage, the first switch means is turned on and the second switch means is turned off, and when the voltage of the applied path is the second voltage, the first switch means is turned on. And a conduction control unit that cuts off and makes the second switch unit conductive.
The control means applies the first voltage, then applies the first voltage, and then applies the first voltage, thereby sequentially performing the detection operation of the plurality of sensors from the upstream side. To do
The sensor control device according to claim 1. Each of the plurality of first sensors further includes holding means for holding a detection result,
The control means may apply the second voltage to cause the conduction control means to shut off the first switch means, and obtain the detection result from the holding means via the application path.
The sensor control device according to claim 11. The detection unit includes a light emitting unit that emits light when the first voltage is applied and a light receiving unit that conducts by receiving light emitted from the light emitting unit,
The holding means includes a third switch means that changes according to the conduction state of the light receiving means,
The control means is connected to the third switch means, and acquires the detection result according to a conduction state of the third switch means.
The sensor control device according to claim 12. A sensor control device,
Storage means for storing the seat,
Image forming means for forming an image on the sheet,
Transport control means for transporting the sheet from the storage means to the image forming means via a transport path,
The sensor control device,
The control means includes a plurality of sensors connected in series to the control means, and a terminating means connected upstream of the control means and downstream of the most downstream sensor of the plurality of sensors. ,
Each of the plurality of sensors performs a detection operation when a first voltage is applied from the control unit, and a second voltage different from the first voltage is applied after the first voltage is applied from the control unit. When applied, the voltage applied from the control means is supplied to the sensor or the terminating means connected to the subsequent stage,
The termination means generates a termination level that is a voltage value different from the detection results of the plurality of sensors,
By repeatedly applying the first voltage and the second voltage, the control unit sequentially performs the detection operation from the upstream sensor and sequentially acquires the detection result of each sensor, and detects the termination level of the termination level. Based on, it is characterized by determining the malfunction of the sensor,
Image forming apparatus. The control means has a recording means for recording the detection results of the plurality of sensors. When the detection result of the most downstream sensor is recorded in the recording means, the conveyance control means detects the number of sensors. Notify that the result recording is completed,
The conveyance control means controls the conveyance of the sheet by reading the detection result recorded in the recording means based on the notification.
The image forming apparatus according to claim 14. The transport control means deletes the read detection result from the recording means,
The image forming apparatus according to claim 15.

Images