JP2016133972A - Communication system and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system that has a configuration in which at least one slave device is connected to a master device, and can improve resistance against external noise compared with a case of transmitting with a constant signal strength; and an image forming apparatus.SOLUTION: A communication system comprises a master device 20 that transmits a signal transmitted from the upstream side to the downstream side, and a slave device 40A that is connected onto the downstream side of the master device 20 and transmits the signal to an execution part connected onto the downstream side to cause the execution part to execute processing corresponding to the signal. The master device 20 includes a log collection part 24 that collects communication information including the state of delay in communication with the slave device 40A, and strength changing means 25 that changes the strength of the signal to be transmitted to the slave device 40A on the basis of the communication information collected by the log collection part 24.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a communication system and an image forming apparatus.

  Conventionally, in order to suppress the occurrence of latency (delay time) required for packet transfer and realize efficient data transfer, a master device and a slave device to which data is transferred from the master device are provided. There has been proposed a data transfer system that measures a data transfer rate based on a transmitted data transfer request, and transmits a restriction request that limits the amount of the data transfer request according to the measured data transfer rate to the master device (for example, Patent Document 1).

JP 2010-218351 A

  An object of the present invention is to provide a communication system and an image forming apparatus capable of improving resistance to external noise as compared with the case where transmission is performed with a constant signal strength in a configuration in which at least one slave device is connected to a master device. It is to provide.

[1] a master device that transmits a signal transmitted from the upstream side to the downstream side;
A slave device connected downstream of the master device and transmitting the signal downstream;
The master device has a recording unit that records communication information indicating a communication state with the slave device in a storage unit;
A communication system, comprising: strength changing means for changing the strength of the signal transmitted from the master device to the slave device based on the communication information recorded in the storage unit.

[2] A master device that transmits a signal transmitted from the upstream side to the downstream side;
A plurality of slave devices connected in series or in parallel to the downstream side of the master device and transmitting the signal downstream;
The master device has a recording unit that records communication information indicating a communication state with the slave device in a storage unit;
First intensity changing means for changing the intensity of the signal transmitted from the master device to the slave device based on the communication information recorded in the storage unit;
The slave devices excluding the slave device connected to the most downstream side, based on the communication information recorded in the storage unit, the strength of the signal transmitted by the master device to the slave device connected to the downstream side Each having second strength changing means for changing
Communications system.

[3] The intensity changing unit changes a threshold for the master device or the slave device to determine whether the signal is on or off when changing the intensity of the signal.
The communication system according to [1] or [2].

[4] The communication system according to any one of [1] to [3], wherein the recording unit of the master device records the communication information in the storage unit in a referable state.

[5] An unshielded cable is used as a cable connecting between the master device and the slave device and between the plurality of slave devices.
The communication system according to any one of [2] to [4].

[6] The communication system according to any one of [1] to [5];
A controller connected to the upstream side of the master device and transmitting the signal to the master device;
The execution unit;
An image forming apparatus.

According to the first and sixth aspects of the invention, in a configuration in which at least one slave device is connected to the master device, it is possible to improve resistance to external noise as compared with the case where transmission is performed with a constant signal strength.
According to the invention which concerns on Claim 2, the intensity | strength of the signal transmitted downstream from the location which received the influence of external noise can be changed.
According to the invention which concerns on Claim 3, compared with the case where a threshold value is not changed, the influence of an external noise can be reduced and it can determine ON / OFF of a signal.
According to the invention which concerns on Claim 4, the occurrence location and cause of communication abnormality can be specified.
According to the invention which concerns on Claim 5, compared with the case where a shielded type cable is used, it becomes possible to reduce the cost of the cable which transmits a signal.

FIG. 1 is a block diagram showing a schematic configuration example of an image forming apparatus to which the communication system according to the first embodiment of the present invention is applied. FIG. 2 is a block diagram illustrating a configuration example of a main part of the communication system according to the first embodiment. 3A and 3B show an example of a transmission / reception unit. FIG. 3A is a circuit diagram of the transmission / reception unit according to the present embodiment for changing the signal strength and transmitting the signal. FIG. 3B is a diagram illustrating transmission with a constant signal strength. It is a circuit diagram of a transmission / reception part. FIG. 4 is a flowchart for changing the communication strength. FIG. 5 is an example of a communication log of communication between a master device and a slave device, (a) is a diagram showing a communication log of signals transmitted from the master device to the slave device, and (b) is from the slave device. It is a figure which shows the communication log of the signal transmitted to a master device. 6A and 6B show signals output from the transmission / reception unit to the differential signal line. FIG. 6A shows a signal in a communication mode with a low signal strength. FIG. 6B shows a signal in a communication mode with a high signal strength. FIG. FIG. 7 is a block diagram showing a configuration example of an image forming apparatus to which the communication system according to the second embodiment of the present invention is applied. FIG. 8 is a block diagram showing a configuration example of an image forming apparatus to which the communication system according to the third embodiment of the present invention is applied.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each figure, about the component which has the substantially same function, the same code | symbol is attached | subjected and the duplicate description is abbreviate | omitted.

[First Embodiment]
FIG. 1 is a block diagram showing a schematic configuration example of an image forming apparatus to which the communication system according to the first embodiment of the present invention is applied.

(Overall configuration of image forming apparatus)
The image forming apparatus 1 is connected to the CPU 10 that generates a signal for controlling each unit of the image forming apparatus 1, the master device 20 that is connected to the CPU 10 and transmits the signal generated by the CPU 10 to the downstream side, and the downstream side of the master device 20. The slave device 40A, a plurality of slave devices 40B to 40E connected in series or in parallel on the downstream side of the slave device 40A, and various data including a communication log, image data, and the like are configured by a memory and a hard disk Storage unit 30. Here, the CPU 10 is an example of a control unit.

  Based on the communication information stored in the storage unit 30, the master device 20 and the slave devices 40A to 40E transmit downstream when the response time exceeds the set value or when the number of retransmissions exceeds the set value. The function of changing the intensity of the signal to be transmitted is provided.

  Various connection modes of the slave devices 40A to 40E can be considered. In the present embodiment, four slave devices 40A to 40D are connected in series to the master device 20, and the slave device 40E is connected in parallel to the slave device 40B. The number and connection of slave devices are not limited to those disclosed in FIG. 1, and the number of slave devices may be one or six or more. Further, three or more slave devices may be connected in parallel downstream of one slave device 40A to 40E. Further, a plurality of slave devices may be connected to the master device 20.

  The “downstream side” means a direction in which a signal is transmitted from the CPU 10 side to the slave devices 40A to 40E side. “Upstream side” means a direction in which a signal is transmitted from the side opposite to the downstream side, that is, from the slave devices 40A to 40E side to the CPU 10 side.

  The “response time” is the time from when the master device 20 transmits a signal to any of the slave devices 40A to 40E until the response is returned from the slave device 40A to 40E to the master device 20, or the slave device 40A. ~ 40E means the time from when a signal is transmitted to the master device 20 until a response is returned from the master device 20 to the slave devices 40A to 40E.

  The “number of retransmissions” means that after either the master device 20 or the slave devices 40A to 40E transmits a signal, a response is returned from either the master device 20 or the slave device 40A to 40E that has received this signal. It means the number of times that the signal is retransmitted every predetermined time.

  The image forming apparatus 1 further includes I / O devices 50A to 50E connected to the downstream sides of the slave devices 40A to 40E, respectively. The I / O devices 50A to 50E are devices such as a development system, a transfer system, a fixing system, a paper transport system, and a recording control system, respectively. The I / O devices 50A to 50E are examples of execution units.

  The I / O devices 50A to 50E execute processing corresponding to development, transfer, fixing, paper transport system, and recording control based on the signals transmitted from the slave devices 40A to 40E. In addition, the I / O devices 50 </ b> A to 50 </ b> E transmit signals indicating a processing state such as processing completion to the CPU 10 via the slave devices 40 </ b> A to 40 </ b> D and the master device 20.

  Signals transmitted by the CPU 10 to the master device 20, slave devices 40A to 40E and I / O devices 50A to 50E, and I / O devices 50A to 50E via the master device 20, slave devices 40A to 40E, and I / O devices 50A to 50E The signal transmitted to the CPU 10 includes various signals.

  That is, various signals include a data signal transmitted to the I / O devices 50A to 50E, an inquiry signal for inquiring about the status of the I / O devices 50A to 50E, and a status notification signal transmitted from the I / O devices 50A to 50E. In addition, a communication status confirmation signal transmitted and received to confirm the communication status between the master device 20 and the slave devices 40A to 40E is included.

  Furthermore, the signal transmitted from the master device 20 to the slave devices 40A to 40E includes designation information that designates the slave devices 40A to 40E that relay the signal as a header. When the slave devices 40A to 40E that have received the signal determine that they are designated based on the designation information, the slave devices 40A to 40E transmit the signal to the I / O devices 50A to 50E.

  In addition, when it is determined that the slave devices 40A to 40C that have received the signal are not designated by themselves based on the designation signal and the downstream slave devices 40B to 40E are designated, the slave devices 40A to 40C are designated as downstream slave devices. It transmits to 40B-40E.

(Master device and slave device)
FIG. 2 is a block diagram illustrating a main part of the communication system according to the first embodiment. In FIG. 2, only the slave devices 40A and 40B are shown, and the other slave devices 40C to 40E and the I / O devices 50C to 50E to be connected are not shown. Since the slave devices 40A to 40E have the same configuration, the slave device 40A will be mainly described below.

  The master device 20 includes a transmission / reception unit 22 that transmits and receives signals between the CPU 10 connected to the upstream side and the slave device 40A connected to the downstream side, and communication indicating a communication state between the master device 20 and the slave device 40A. A log generation unit 23 for generating a log; a communication log generated by the log generation unit 23; and a log collection unit 24 for storing communication logs collected from the slave devices 40A to 40E in the storage unit 30, and the master device 20 and the slave device And a control unit 21 that controls the slave devices 40A to 40E (only the slave devices 40A and 40B are illustrated in FIG. 2). Here, the log collection unit 24 is an example of a recording unit, and the communication log is an example of communication information.

  The master device 20 is configured to transmit a signal to the slave devices 40A to 40E and retransmit the signal to the slave devices 40A to 40E when a response is not returned from the slave devices 40A to 40E within a predetermined time.

  A plurality of differential signal lines 100, signal lines 101, and ground lines 102 are connected between the master device 20 and the slave device 40A and between the slave devices 40A to 40E. The plurality of differential signal lines 100 each include at least one differential signal line (a pair) for transmitting a signal from the upstream side to the downstream side and a differential signal line for transmitting the signal from the downstream side to the upstream side. Yes. The signal line 101 is used to notify the signal strength mode. The differential signal line 100 is, for example, a twisted pair cable. However, the present invention is not limited to this, and other cables can be used as long as they are cables that transmit differential signals.

  The slave device 40A includes a control unit 41 that controls each unit of the slave device 40A, a master device 20 connected to the upstream side, and a transmission / reception unit 42 that transmits and receives signals between the slave device 40B connected to the downstream side, A log generation unit 43 that generates a communication log indicating a communication state between the master device 20 and the slave device 40B.

  Similar to the master device 20, the slave devices 40 </ b> A to 40 </ b> E are configured to transmit a signal to the master device 20 and retransmit the signal to the master device 20 when a response is not returned within a certain time.

  The slave devices 40A to 40E relay the signal transmitted from the master device 20 to the I / O devices 50A to 50E.

  The transmission / reception unit 22 of the master device 20 includes an intensity changing unit 25 that changes the signal intensity of a signal output to the differential signal line 100 connected to each of the downstream slave devices 40A to 40E. Details of the strength changing unit 25 will be described later.

  Each of the slave devices 40A to 40C includes an intensity changing unit 45 that changes the intensity of a signal output to the differential signal line 100 connected to the slave devices 40B to 40E on the downstream side of itself. The strength changing unit 25 of the master device 20 is an example of a first strength changing unit, and the strength changing unit 45 of the slave devices 40A to 40E is an example of a second strength changing unit.

  The log generation unit 23 of the master device 20 includes a counter 231 that counts the number of retransmissions until responses to signals transmitted to the downstream slave devices 40A to 40E are returned from the slave devices 40A to 40E, and the slave devices 40A to 40E. And a timer 232 for measuring a response time from when a signal is transmitted to when a response to the signal is returned to the master device 20. The log generation unit 23 generates a communication log including a delay state, that is, the number of retransmissions and a response time.

  The log generation unit 43 of the slave devices 40 </ b> A to 40 </ b> E transmits a signal to the master device 20 and a counter 441 that counts the number of retransmissions performed until a response to the signal transmitted to the master device 20 is returned from the master device 20. A timer 432 for measuring a response time until a response to the signal is returned. The log generation unit 43 generates a communication log including a delay state, that is, the number of retransmissions and a response time.

  The log collection unit 24 of the master device 20 collects the communication log generated by the log generation unit 23 of the master device 20 and the communication log generated by the log generation unit 43 of the slave devices 40A to 40E. The log collection unit 24 stores the communication log in the storage unit 30 as history information in a text format or the like that can be referred to by the administrator of the image forming apparatus 1.

  For example, as illustrated in FIGS. 5A and 5B, the log collection unit 24 includes a communication log Log1 indicating delay information in signals transmitted from the master device 20 to the slave devices 40A to 40E, and the slave devices 40A to 40A. A communication log Log 2 indicating delay information in the signal transmitted from 40E to the master device 20 is recorded in the storage unit 30. The communication logs Log <b> 1 and Log <b> 2 are recorded in the storage unit 30 by being divided for each slave device 40 </ b> A to 40 </ b> E so as to be easily browsed.

  By storing the communication logs Lo1 and Log2 in the storage unit 30 so that they can be browsed, when a communication abnormality occurs, an administrator or the like uses the communication log to identify the location and cause of the communication abnormality. The image forming apparatus 1 can be quickly and appropriately treated.

  The control unit 21 of the master device 20 refers to the communication log stored in the storage unit 30 at regular intervals, and sets the differential signal line 100 between the master device 20 and the slave device 40A or between the slave devices 40A to 40E. It is determined whether a communication error has occurred. In addition, when the control unit 21 of the master device 20 determines that a communication abnormality has occurred, the controller 21 identifies a location where the communication abnormality has occurred based on the communication log, and the upstream master device 20 or slave device from the location. The communication mode of signals transmitted from 40A to 40C is switched from a communication mode with a low signal strength to a communication mode with a high signal strength.

(Transceiver)
FIG. 3 shows an example of the transmission / reception unit. (A) is a circuit diagram of the transmission / reception unit 22 of the present embodiment that transmits the signal with the intensity changed, and (b) shows a constant signal strength. It is a circuit diagram of the transmission / reception part of the comparative example which transmits.

  The transmission / reception unit 22 of the master device 20 includes a differential amplifier 221 that differentially amplifies a signal output from the control unit 21 and the like, and an intensity changing unit 25. The intensity changing unit 25 includes first and second paths 252 and 253 that connect the differential amplifier 221 and the differential signal line 100, and switches 254a to 254d that switch between the first path 252 and the second path 253. Is provided. The switches 254 a to 254 d have contacts a 1, a 2, contacts b 1, b 2, contacts c 1, c 2 and contacts d 1, d 2, respectively, and switch each contact according to the control of the control unit 21. The switches 254a to 254d are, for example, semiconductor switches, but relay circuits or the like may be used.

  The transmission / reception unit 22A of the comparative example shown in FIG. 3 (b) includes an upstream transmission / reception unit 22A and a downstream transmission unit 42A by a cable 200 in which the differential signal line 100 is covered with a shield 103 in order to improve noise resistance. Is connected. The shield 103 is connected to the ground GND to shield external noise, and suppresses noise from entering the differential signal line 100. However, in the configuration using the cable 200 having the shield 103, noise resistance can be improved, but the cost of the cable increases, which causes a problem that the cost of the image forming apparatus 1 is increased.

  On the other hand, the intensity changing unit 25 according to the present embodiment switches the switches 254a to 254d based on the control of the control unit 21, and converts the differential signal that has passed through the first path 252 or the second path 253 to the differential signal. By outputting to the slave device 40A via the line 100, it is possible to improve noise resistance even when an unshielded cable without a shield is used. Therefore, the response time and the number of retransmissions can be reduced, and the master device 20 and the slave devices 40A to 40E can transmit the signals transmitted from the CPU 10 to the I / O devices 50A to 50E at high speed and reliably. .

  The first path 252 of the strength changing unit 25 includes a signal line 252a that connects the contact point a1 of the switch 254a and the contact point c1 of the switch 254c, and a signal line 252b that connects the contact point b1 of the switch 254b and the contact point d1 of the switch 254d. The signal output from the differential amplifier 221 is directly output to the differential signal line 100.

  The second path 253 of the strength changing unit 25 includes a signal line 253a that connects the contact point a2 of the switch 254a and the contact point c2 of the switch 254c, and a signal line 253b that connects the contact point b2 of the switch 254b and the contact point d2 of the switch 254d. Consists of. The second path 253 is provided with a shunt circuit 255 that shunts a part of the current of the signal output from the differential amplifier 221. The second path 253 outputs the signal shunted by the shunt circuit 255 to the differential signal line 100.

  The shunt circuit 255 of the second path 253 includes a resistor R1 provided on the signal line 253a and a resistor R2 provided on a line connecting the signal line 253a and the signal line 253b, and the resistors R1 and R2 Based on the resistance value ratio, the intensity of the signal output from the differential amplifier 221, that is, the current value is reduced and output to the differential signal line 100.

  The transmission / reception units 42 of the slave devices 40A to 40E are not shown in FIG. 3A, but, like the transmission / reception unit 22 of the master device 20, the differential amplifier, the first path, and the second path And an intensity changing unit 45 having switches a to d.

(Operation of image forming apparatus)
Next, an example of the operation of the image forming apparatus 1 will be described. FIG. 4 is an example of a flowchart for changing the signal strength. FIG. 5 is an example of a communication log in communication between the master device 20 and the slave devices 40A to 40E. (A) is a communication log of signals transmitted from the master device 20 to the slave devices 40A to 40E. Is a communication log of signals transmitted from the slave devices 40A to 40E to the master device 20. 6A and 6B show signals output from the transmission / reception units 22 and 42 to the differential signal line 100, FIG. 6A shows a signal in a communication mode with a low signal strength, and FIG. 6B shows a communication mode with a high signal strength. It is a figure which shows the signal of.

  When the power is turned on and the image forming apparatus 1 is operating, the master device 20 detects the differential signal line 100 between the master device 20 and the slave device 40A or the differential between the slave devices 40A to 40E at regular intervals. It is determined whether or not a communication abnormality has occurred in the signal line 100, and the signal strength is changed based on this determination. It is assumed that a communication mode with a small signal strength is set as an initial setting when power is turned on, and a threshold value is set to a small value.

  The control unit 21 of the master device 20 determines whether or not the response time exceeds the set value (S1). That is, the control unit 21 of the master device 20 refers to the communication log stored in the storage unit 30, and after the master device 20 transmits a signal to any of the slave devices 40 </ b> A to 40 </ b> E, The response time until the response is returned to the master device 20, or after any of the slave devices 40A to 40E transmits a signal to the master device 20, the response from the master device 20 is returned to any of the slave devices 40A to 40E. It is determined whether or not the response time until the time exceeds the set value.

  For example, when the set value of the response time is 100 ms, in the communication log Log2, the response time from when the master device 20 transmits a signal to the slave device 40E until the response is returned from the slave device 40E to the master device 20 is 120 ms. Since the response time between the other slave devices 40A to 40D is less than 100 ms, the control unit 21 of the master device 20 determines that a communication abnormality has occurred between the slave device 40B and the slave device 40E. To do.

  When the control unit 21 of the master device 20 determines that the response time does not exceed the set value (S1: No), the master device 20 retransmits the signal until the response is returned from the slave devices 40A to 40E, Alternatively, the slave devices 40A to 40E determine whether or not the number of retransmissions that the slave devices 40A to 40E have retransmitted the signal before the response is returned from the master device 20 exceeds the set value (S2).

  For example, when the set value of the number of retransmissions is 3, in the communication log Log1, the number of retransmissions until the response is returned from the slave device 40E is 5, and the response is returned from the other slave devices 40A to 40D. Since the number of retransmissions until the transmission is less than 3, the control unit 21 of the master device 20 determines that a communication abnormality has occurred between the slave device 40B and the slave device 40E. Further, in the communication log Log2, since the number of retransmissions of the slave device 40E is the same as the set value, the control unit 21 determines that no communication abnormality has occurred between the slave device 40B and the slave device 40E. To do.

  The control unit 21 may determine that a communication abnormality has occurred when the response time or retransmission time of both the communication log Log1 and the communication log Log2 exceeds the set value in steps S1 and S2. Alternatively, it may be determined that a communication error has occurred when one of the retransmission time or the response time of the communication log Log1 and the communication log Log2 exceeds a set value.

  When the control unit 21 of the master device 20 determines that the number of retransmissions does not exceed the set value (S2: No), the master communication device 21 transmits a signal to the slave devices 40A to 40E in the communication mode in which the current communication mode is high in signal strength. It is determined whether or not (S3).

  When the control unit 21 determines that a signal is transmitted to the downstream slave devices 40A to 40E in the communication mode with a small signal strength (S3: No), the process is completed.

  On the other hand, if the control unit 21 of the master device 20 determines that a signal is being transmitted to the slave devices 40A to 40E on the downstream side in the communication mode with a large signal strength (S3: Yes), the strength changing unit 25 of the master device 20 or The intensity changing unit 45 of the slave devices 40A to 40E is controlled to change to a communication mode with a low signal intensity (S4).

  That is, the control unit 21 sets the strength (voltage) of the signal transmitted from the transmitting / receiving unit 22 of the master device 20 to the slave devices 40A to 40E on the downstream side in the communication mode (for example, the signal level) shown in FIG. From the minimum voltage value of −5V and the maximum value of 5V) to the communication mode with a small signal strength shown in FIG. 6A (for example, the minimum value of the signal voltage is −2.5V and the maximum value is 2.5V). To change.

  Further, the controller 21 determines whether the signal is on or off by setting the voltage of the signal line 101 to a low level. The threshold value shown in FIG. 6B is set to a large value (for example, −4.5 V, 4.5 V). ) To a small value (for example, −2V, 2V) shown in FIG. 6A (S5).

  When the control unit 21 of the master device 20 determines that the response time exceeds the set value (S1: Yes), or when it determines that the number of retransmissions exceeds the set value (S2: Yes), the transmission / reception unit 22 Alternatively, the signal transmitted from the transmission / reception unit 42 to the downstream slave devices 40A to 40E is changed to a communication mode with a high signal strength (S6).

  That is, the control unit 21 changes the strength (voltage) of the signal transmitted from the transmission / reception unit 22 or 42 to the slave devices 40A to 40E on the downstream side from the communication mode with small signal strength shown in FIG. ) To change to a communication mode with a large signal strength shown in FIG.

  After changing the signal to be transmitted to a communication mode with a high communication strength (S6), the control unit 21 sets the voltage of the ground line 102 to a high level and sets the communication mode with a high signal strength to the control unit 41 of the slave devices 40A to 40E. The control unit 41 changes the threshold for determining whether the signal is on or off from a small value to a large value (S7).

[Second Embodiment]
FIG. 7 is a block diagram showing a schematic configuration example of an image forming apparatus to which the communication system according to the second embodiment of the present invention is applied.

  In the first embodiment, only the master device 20 has the log collection unit 24. However, in this embodiment, the master device 20 and the slave devices 40A to 40E have the log collection units 24 and 44. This is different from the first embodiment. The following description will focus on differences from the first embodiment.

  The image forming apparatus 1 according to the present embodiment includes a master device 20 and slave devices 40A to 40E. Each of the slave devices 40A to 40E has a log collection unit 44 that collects a communication log between the slave devices 40A to 40E and a communication log between the master device 20 and the slave devices 40A to 40E, respectively. The log collection unit 44 of the slave devices 40 </ b> A to 40 </ b> E stores the collected communication log in the storage unit 30 via the differential signal line 100.

  The control unit 41 of the slave devices 40A to 40C refers to the communication log stored in the storage unit 30, and whether or not a communication abnormality has occurred in the differential signal line 100 between the slave devices 40B to 40E on the downstream side. Determine whether. When the control unit 41 determines that a communication abnormality has occurred in the differential signal line 100, the control unit 41 changes the communication mode via the differential signal line 100 in which the communication abnormality has occurred to a large communication mode. Note that the control unit 41 may determine whether a communication abnormality has occurred in the differential signal line 100 between the I / O devices 50A to 50E.

[Third Embodiment]
FIG. 8 is a block diagram showing a schematic configuration example of an image forming apparatus to which the communication system according to the third embodiment of the present invention is applied.

  In the first embodiment, the signal line 101 is used as a line connecting the master device 20 and the slave device 40A and between the slave devices 40A to 40E. However, in the present embodiment, the signal line 101 is provided. This is different from the first embodiment in that this is not done. The following description will focus on differences from the first embodiment.

  When the image forming apparatus 1 according to the present embodiment is turned on, the control unit 21 of the master device 20 transmits a signal to the slave devices 40A to 40E and sets identification numbers for identifying the slave devices 40A to 40E. To do. At this time, the log collection unit 24 of the master device 20 collects communication logs from the master device 20 and the slave devices 40A to 40E and records them in the storage unit 30.

  Based on the communication log recorded in the storage unit 30, the control unit 21 of the master device 20 determines the differential signal line depending on whether the response time exceeds the set value or whether the number of retransmissions exceeds the set value. It is determined whether a communication abnormality has occurred in 100. When it is determined that a communication abnormality has occurred in the differential signal line 100, the control unit 21 outputs a signal to the master device 20 or the slave devices 40A to 40C that output signals to the differential signal line 100 in which the communication abnormality has occurred. A command signal for setting the communication mode with a high strength is transmitted.

  The master device 20 or the slave devices 40A to 40E that have received the command signal control the strength changing units 25 and 45 to change the communication mode to a communication mode with a high signal strength. In addition, the slave devices 40A to 40E that have received a command signal for setting the communication mode to a communication mode with a high signal strength set a large threshold value for determining whether the received signal is on or off.

[Modification]
The embodiments of the present invention are not limited to the above-described embodiments, and various modifications and implementations are possible without departing from the scope of the present invention. For example, the strength changing units 25 and 45 of the master device 20 or the slave devices 40A to 40E may change the signal strength of three or more stages based on the number of communication log retransmissions or the response time.

  Further, the intensity changing units 25 and 45 of the master device 20 or the slave devices 40A to 40E change the signal intensity linearly by controlling the current value of the signal to be transmitted based on the number of retransmissions of the communication log or the response time. May be.

  Further, the signal line between the master device 20 and the slave devices 40A to 40E is not limited to the differential signal line, and may transmit and receive signals by single-ended transmission. A common signal line may be used for upstream communication and downstream communication.

  In addition, the master device 20 and the slave devices 40A to 40E may be configured to detect noise mixed in the differential signal line 100 and change the communication mode to a communication mode with high signal strength when noise is detected.

  Further, when the slave devices 40A to 40E determine that a communication abnormality has occurred in any of the differential signal lines 100, the signals transmitted to the upstream master device 20 or the slave devices 40A to 40C have high signal strength. The communication mode may be changed.

  When it is determined that a communication error has occurred in any of the differential signal lines 100, signals transmitted and received between all the master devices 20 and the slave devices 40A to 40E are set to a communication mode with a high communication strength. It may be changed.

  In addition, for example, it is possible to omit some of the constituent elements of the above-described embodiment within a range not changing the gist of the present invention, and in the flow of the above-mentioned embodiment, addition, deletion, change, replacement, etc. of steps Is possible.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... CPU, 20 ... Master device, 21 ... Control part, 22, 22A ... Transmission / reception part, 23 ... Log generation part, 24 ... Log collection part, 25 ... Strength change part, 30 ... Storage part, 40A ˜40E, slave device, 41, control unit, 42, 42A, transmission / reception unit, 43, log generation unit, 43, log collection unit, 45, intensity changing unit, 50A-50E, I / O device 50, 100, differential Signal line 101 ... Signal line 102 ... Ground line 103 ... Shield 200 ... Cable 221 ... Differential amplifier 231 ... Counter 232 ... Timer 252 ... First path 252a, 252b ... Signal line 253 2nd path, 253a, 253b ... signal line, 254a-254d ... switch, 255 ... shunt circuit, 432 ... timer, 441 ... counter, a1-d1 ... contact, 2~d2 ... contact, Log1, Log2 ... communication log, R1, R2 ... resistance

Claims (6)

A master device that transmits a signal transmitted from the upstream side to the downstream side;
A slave device connected downstream of the master device and transmitting the signal downstream;
The master device has a recording unit that records communication information indicating a communication state with the slave device in a storage unit;
A communication system, comprising: strength changing means for changing the strength of the signal transmitted from the master device to the slave device based on the communication information recorded in the storage unit. A master device that transmits a signal transmitted from the upstream side to the downstream side;
A plurality of slave devices connected in series or in parallel to the downstream side of the master device and transmitting the signal downstream;
The master device has a recording unit that records communication information indicating a communication state with the slave device in a storage unit;
First intensity changing means for changing the intensity of the signal transmitted from the master device to the slave device based on the communication information recorded in the storage unit;
The slave devices excluding the slave device connected to the most downstream side, based on the communication information recorded in the storage unit, the strength of the signal transmitted by the master device to the slave device connected to the downstream side Each having second strength changing means for changing
Communications system. The strength changing means changes a threshold for the master device or the slave device to determine whether the signal is on or off when changing the strength of the signal.
The communication system according to claim 1 or 2.   The communication system according to any one of claims 1 to 3, wherein the recording unit of the master device records the communication information in the storage unit in a state where the communication information can be referred to. Using a non-shielded cable as a cable connecting between the master device and the slave device and between the plurality of slave devices,
The communication system according to any one of claims 1 to 4. A communication system according to any one of claims 1 to 5;
A controller connected to the upstream side of the master device and transmitting the signal to the master device;
An execution unit connected to the downstream side of the slave device and executing processing based on a signal transmitted from the slave device;
An image forming apparatus.

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