JP2014084209A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce maintenance workload when abnormality relating to any of plural rollers driven by one motor occurs.SOLUTION: An image formation device comprises: N sets of transportation rollers; a motor which is a common drive source for the rollers; a paper sensor to detect existence or nonexistence of a paper at a detecting position upstream of the rollers on a transportation path; a memory to store a threshold value; means to monitor transition of a drive current value of the motor during transportation; means to measure time length of a period from a time when a paper is detected by the paper sensor to a time when the drive current value becomes the threshold value or lower after exceeding the threshold value; means to identify the abnormality-relating roller from the N sets of rollers based on transportation time from the detecting position to the arrangement position of each roller and the length of the measured period; and means to output abnormality-notifying information showing the identified roller.

Description

  The present invention relates to an image forming apparatus that prints an image on a sheet.

  An image forming apparatus such as a printer or an MFP (Multi-functional Peripheral) prints an image on a sheet while moving a sheet of sheets at a constant speed along a conveyance path from a sheet table to a sheet discharge port. Roller pairs are arranged at predetermined intervals in the transport path, and the paper is sandwiched between the roller pairs rotated by a motor and sent downstream. The arrangement interval of the roller pairs is shorter than the minimum sheet length in the transport direction determined by the specification of the adaptive sheet size, and the sheet being transported is sandwiched between the downstream roller pair before leaving the upstream roller pair.

  There is a technique for detecting an abnormality in a mechanism that transmits a driving force of a motor. The electrophotographic copying machine described in Patent Document 1 includes an abnormality detection device. This abnormality detection device detects an abnormality in the drive transmission mechanism composed of a plurality of gears having different numbers of teeth by a change in the rotational speed of the motor, and which gear is abnormal is determined by the cycle of the rotational speed change. Identify based on.

  Patent Document 2 describes that in an apparatus for cleaning a filter of an air conditioner, it is determined whether maintenance is necessary based on a driving current value of a motor. The apparatus of the document reports that it is a maintenance time when the driving current value of the motor, which increases as the filter stain progresses, exceeds a predetermined threshold value.

JP 2006-340423 A JP 2009-250449 A

  A mechanism configuration in which a plurality of roller pairs for paper conveyance is driven by a single motor is common. This is because the use of a common drive source facilitates rotational speed control and is advantageous in terms of manufacturing cost. However, when such a configuration is adopted, an abnormality in the transport system can be detected only by comparing the drive current value of the motor with the threshold value as disclosed in Patent Document 2, but naturally, which abnormality is detected. It is not possible to specify whether the roller pair is involved.

  Further, in the case of the configuration in which the driving force of the motor is transmitted to each of the plurality of roller pairs via the same transmission mechanism, the technique of Patent Document 1 that identifies the abnormal location based on the period of the rotational speed change of the motor has an abnormality. It cannot be specified which roller pair is involved. This is because there is almost no difference in the period of the rotational speed change at the time of abnormality among a plurality of roller pairs.

  For this reason, there has been a problem that a person in charge of maintenance work that replaces or cleans rollers or gears sometimes takes time when work is abnormal.

  In view of such circumstances, an object of the present invention is to reduce a maintenance work load when an abnormality relating to any of a plurality of rollers driven by a single motor occurs.

  An apparatus that achieves the above-described object is an image forming apparatus that prints an image on a sheet, and is used for conveying N pieces (N is an integer of 2 or more) arranged at intervals on a conveyance path through which the sheet passes. A roller, a motor that is a common drive source for the N rollers, a paper sensor that detects the presence or absence of paper at a detection position upstream of the position where the N rollers are disposed on the transport path, A memory for storing a threshold value for determining whether or not the sheet is conveyed correctly based on a driving current value of the motor, means for monitoring a transition of the driving current value of the motor during conveyance, and the presence of the sheet by the sheet sensor. Means for measuring the length of the period from the time when the driving current value exceeds the threshold and then becomes equal to or less than the threshold, from the detection position Based on the transport time to the arrangement position of each of the rollers and the measured length of the period, means for identifying a roller involved in the abnormality among the N rollers, and an abnormality indicating the identified roller Means for outputting notification information.

  According to the present invention, it is possible to reduce a maintenance work load when an abnormality relating to any of a plurality of rollers driven by a single motor occurs.

1 is a diagram illustrating a schematic hardware configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration of a part related to detection of abnormality in paper conveyance in the image forming apparatus. FIG. 10 is an explanatory diagram of a paper transport abnormality detection method. It is a flowchart which shows the outline | summary of the procedure of abnormality detection. FIG. 6 is a diagram illustrating a state of each roller position in a paper transport process. It is a flowchart which shows the procedure which sets the threshold value for discriminating the presence or absence of abnormality. It is a figure which shows the example of a threshold value setting. It is a figure which shows transition of the drive current value of the motor when a sheet | seat is normally conveyed. It is a figure which shows transition of the drive current value of a motor when conveyance by A roller is abnormal. It is a figure which shows transition of the drive current value of a motor when conveyance by B roller is abnormal. It is a figure which shows transition of the drive current value of a motor when conveyance by C roller is abnormal. It is a figure which shows transition of the drive current value of a motor in case conveyance by A roller and conveyance by B roller are abnormal. It is a figure which shows transition of the drive current value of a motor when conveyance by B roller and conveyance by C roller are abnormal. It is a figure which shows transition of the drive current value of a motor in case conveyance by A roller and conveyance by C roller are abnormal. 6 is a flowchart of a conveyance abnormality detection process executed by the image forming apparatus. It is a flowchart of the abnormal part specific routine in a conveyance abnormality detection process.

  An image forming apparatus 1 shown in FIG. 1 is an MFP (Multi-functional Peripheral) having various functions other than a printing function and printing. The image forming apparatus 1 is given a print job by a direct operation using the operation panel 22 and an access from an external device via a network (not shown).

  A main controller 10 responsible for overall control of the image forming apparatus 1 includes a CPU (Central Processing Unit) 11 as a computer for executing control programs and various applications, a ROM (Read Only Memory) 12 for storing control programs, and a program execution work. It has a RAM (Random Access Memory) 13 serving as an area, and a battery-backed NV-RAM (nonvolatile memory) 14 for storing setting data necessary for control.

  The operation panel 21 has a display 215 that displays an operation screen. An ADF (Auto Document Feeder) 22 conveys a document sheet to a reading position in the image scanner 23 in copying, image input, or facsimile transmission. The image scanner 23 optically reads image information recorded on the document sheet. The printer controller 24 controls the operation of the printer engine 25. The printer engine 25 prints a monochrome or color image by electrophotography on one or both sides of the paper supplied from the multistage paper stacker 26. The communication interface 27 connects the image forming apparatus 1 to a network for communication with an external apparatus. The modem 28 is used for facsimile communication via a public telephone line. The storage 29 is a mass storage device such as a hard disk drive (HDD). The storage 29 is used as a medium for storing a control program, control data, and various documents. Data and programs stored in the storage 29 are loaded into the work area as necessary.

  As illustrated in FIG. 2, the image forming apparatus 1 includes a conveyance path 50 through which a sheet used for printing passes. Rollers 41, 42, and 43 are arranged at predetermined intervals along the conveyance path 50, and rollers 41b, 42b, and 43b are arranged so as to face the rollers 41, 42, and 43 one by one. A pair of opposing rollers sandwich the paper, and the paper is conveyed by the rotation of the rollers. Hereinafter, in order to distinguish the illustrated three roller pairs, for convenience, the pair of rollers 41 and 41b is referred to as “A roller”, the pair of rollers 42 and 42b is referred to as “B roller”, and the rollers 43 and 43b. This pair is sometimes referred to as a “C roller”. The A roller, B roller, and C roller may be collectively referred to as a conveyance roller. In addition, the position where the A roller is arranged in the conveyance path 50 (strictly, the position where the nip portion is formed) is called “A position”, the position where the B roller is arranged is called “B position”, and the C roller. The position at which is placed may be referred to as “C position”.

  A rotational driving force is transmitted to the A roller, the B roller, and the C roller through a gear from a motor 40 that is a common driving source. The configuration of gears interposed between each roller and the motor 40 is selected according to the positional relationship between the shaft of the motor 40 and each roller so that the rotational peripheral speeds of these rollers are the same.

  In the image forming apparatus 1, a current detection circuit 465 is incorporated in a motor driver 46 that supplies a drive current to the motor 40 in order to detect an abnormality in the transport mechanism that is driven by the motor 40. The current detection circuit 465 outputs a detection signal indicating the magnitude (drive current value) of the drive current supplied to the motor 40 to the transport control unit 47. The conveyance control unit 47 determines the presence or absence of abnormality by comparing the drive current value I of the motor 40 obtained by the current detection circuit 465 with a threshold value Ith stored in the memory 475 in advance. The transport control unit 47 includes the main controller 10 and the printer controller 24.

  Upon execution of a print job, upon receiving a drive instruction from the conveyance control unit 47, the motor driver 46 supplies drive power to the motor 40 and adjusts the drive current so as to maintain rotation at a predetermined speed. In the state where the conveyance roller sandwiches the paper, the force for suppressing the rotation of the roller is larger than in the state where the paper is not. That is, the load on the motor 40 is large. The drive current value I of the motor 40 increases as the load increases.

  Normally, the load on the motor 40 increases as the conveyance roller deteriorates. Typical degradation appears as distortion of the peripheral shape of the transport roller. One cause of the distortion is that the accumulated time of contact with the paper is not necessarily uniform within the roller circumferential surface. A portion that is in contact with the paper for a long time is easily deformed flat.

  The load on the motor 40 is increased not only with the change with time but also when a sudden failure occurs. Examples of defects include cracks on the roller peripheral surface, gear breakage, and adhesion of foreign matter to the gear.

  The conveyance control unit 47 detects a state where the drive current value I exceeds the threshold value Ith as an abnormality of the conveyance mechanism. The threshold value Ith is set so that the state can be detected as abnormal when the deterioration progresses to exceed the allowable range.

  In the image forming apparatus 1, when an abnormality of the transport mechanism is detected, it is specified which of the A position, the B position, and the C position is the abnormal part. For example, when the abnormal location is the A position, the malfunction may be in the A roller or in the gear that transmits the driving force to the A roller. However, in practice, there is a high probability that the A roller is defective.

  The paper sensor 52 disposed upstream of the position A in the transport path 50 is used for specifying the abnormal part. The paper sensor 52 outputs a detection signal corresponding to the presence or absence of paper at the detection position where the paper sensor 52 is disposed to the conveyance control unit 47. The memory 475 of the transport control unit 47 stores transport times Ta, Tb, Tc corresponding to distances Da, Db, Dc from the detection position (paper sensor position) of the paper sensor 52 to each roller position. As will be described later, the conveyance control unit 47 identifies an abnormal location based on the relationship between the change in the drive current value I and the conveyance times Ta, Tb, and Tc.

In FIG. 3 (A), the roller for conveyance is each arrange | positioned at N roller positions including A position, B position, and C position on a conveyance path. When the distance from the paper sensor position to each roller position is Da, Db, Dc,..., Dn and the transport speed is V, the transport times Ta, Tb, Tc,. It is expressed by the following formula.
Ta = Da / V
Tb = Db / V
Tc = Dc / V
Tn = Dn / V
FIG. 3B shows a state where two sheets of paper P are being conveyed. The paper length S of the paper P is smaller than the distance between the roller positions. The two sheets P are conveyed with a sheet interval W provided.

  In FIG. 3C, the states of the A position and the B position at a plurality of time points during the conveyance of the two sheets of paper P are shown. At time t1, the leading edge of the first sheet P has just reached the B position, and the first sheet P exists at the A and B positions. At time t2, the trailing edge of the first sheet P has just passed the A position, the sheet P does not exist at the A position, and the first sheet P exists at the B position. At time t3, the trailing edge of the first sheet P has just passed the B position, the sheet P does not exist at the B position, and the second sheet P exists at the A position. At time t4, the leading edge of the second sheet P has just reached the B position, and the second sheet P exists at the A and B positions.

  FIG. 3D shows a change in load applied to the motor when it is assumed that the conveyance by the B roller is abnormal in the conveyance of the two sheets P as shown in FIG. At time t1, the load increases due to the sheet P being sandwiched between the B rollers. After that, while the paper P is sandwiched between the B rollers, the load increases. When the paper P passes the B position at time t3, the load decreases. While there is no sheet P in the B position, the load continues to decrease. When the B roller sandwiches the second sheet P at time t4, the load increases again.

  Identification of the abnormal part is performed by utilizing a phenomenon in which the load decreases when the load once increases and then there is no sheet at the roller position corresponding to the abnormal part. Since the timing at which the load decreases differs depending on which roller position is the abnormal location, the abnormal location can be identified based on the known relationship between the timing at which the load decreases and the roller position.

  The flowchart of FIG. 4 shows an outline of the abnormality detection procedure. Timekeeping is started from the time when the paper being conveyed reaches the paper sensor position as the reference position (# 1). The drive current value I that changes according to the load on the motor 40 is measured (# 2), and when the drive current value I exceeds the threshold Ith (YES in # 3), it waits for the drive current value I to decrease (#). 4).

  When the drive current value I decreases (YES in # 4), the measured time is compared with the above-described transport times Ta, Tb, Tc,... Tn corresponding to each of the plurality of roller positions calculated in advance (# 5). ). Then, the roller position corresponding to the conveyance time closest to the time measured is specified as an abnormal location (abnormal roller position) (# 6).

  Hereinafter, the detection operation of the conveyance abnormality in the image forming apparatus 1 will be described in more detail.

  FIG. 5 shows a plurality of states distinguished according to the presence / absence of paper at the A position, the B position, and the C position. The conveyed sheets P1, P2, and P3 are sheets of the same size, and have a sheet length longer than the distance from the A position to the C position.

  State [1] is a state at the time when the leading edge of the first sheet P1 has passed the A position, and is a state where the sheet exists only at the A position of the three roller positions. In state [1], there is a sheet at the sheet sensor position.

  State [2] is a state when the leading edge of the first sheet of paper P1 has passed the B position, and is a state in which a sheet exists at the A and B positions of the three roller positions. In state [2], there is a sheet at the sheet sensor position.

  The state [3] is a state at the time when the leading edge of the first sheet P1 has passed the C position, and is a state in which the sheet exists at all of the A position, the B position, and the C position. In state [3], there is no paper at the paper sensor position.

  State [4] is a state at the time when the trailing edge of the first sheet of paper P1 has passed through position A, and is a state in which sheets are present at positions B and C among the three roller positions. In state [4], there is a second sheet at the sheet sensor position.

  The state [5] is a state at the time when the rear end of the first sheet P1 passes the B position, and is a state where the sheet exists at the A position and the C position among the three roller positions. In state [5], there is a second sheet at the sheet sensor position.

  When a plurality of sheets P1, P2, and P3 are conveyed one after another as shown in the drawing, after the state [5], any one of the states [2] to [5] appears instead of the state [1]. To do.

  The flowchart of FIG. 6 shows a procedure for setting a threshold value Ith for determining whether there is an abnormality. The threshold value Ith is set based on the measurement result of the drive current value I using an image forming apparatus of the same model as the image forming apparatus 1 before the image forming apparatus 1 is shipped from the factory that manufactures it. It is stored in the memory 475 of the device 1.

  First, the structure information of the transport mechanism, the information on the paper to be used, and the transport control information are acquired (# 11, # 12, # 13). The structure information includes the number N of transport rollers (3 in this example) and distances Da, Db, and Dc from the paper sensor position to each roller position. The paper information is a paper length S and a paper type (thickness). The conveyance control information is a conveyance speed V and a sheet interval (inter-sheet) W.

  The maximum number n of rollers that can contact the paper to be used at the same time is calculated (# 14), and the above-described transport times Ta, Tb, and Tc, which are required time for transport from the paper sensor position to each roller position, are calculated. (# 15). The maximum number n is determined by the distance between the sheet length S and the roller position. In the example of FIG. 5, the maximum number n is 3 which is the same as the number N of rollers.

  Next, the drive current value I of the motor 40 that is being transported in the apparatus condition where the transport is normally performed is continuously measured (# 16). Then, the drive current value I at a specific time determined from the change in the drive current value I and the transport times Ta, Tb, and Tc is set to the threshold Ith (# 17). A value allowing a predetermined margin in the drive current value I at a specific time may be set as the threshold value Ith. The specific time is a time when the sheet straddles (n-1) roller positions, which is one less than the maximum number n described above. According to the example of FIG. 5, the time when the state [2], the state [4], and the state [5] are reached is a specific time.

  A control table for associating the set threshold value Ith with the combination of the sheet length S and the sheet type is created (# 18). The procedure from step # 12 to step # 18 is performed for a plurality of paper sizes and a plurality of paper types suitable for the image forming apparatus 1, and is applied to each of the assumed combinations of paper length S and paper types. The threshold Ith is obtained to complete the control table. The completed control table is stored in the memory 475.

  When the image forming apparatus 1 shipped from the factory is used by the user, the image forming apparatus 1 extracts the threshold value Ith corresponding to the paper size and paper type specified by the print job from the control table, and the conveyance mechanism. Applies to detection of abnormalities and identification of abnormalities.

  FIG. 7 shows an example of threshold setting. As shown in the timing chart at the top of the drawing, when a plurality of sheets are conveyed, the output of the sheet sensor 52 is switched from the absence of sheets to the presence of sheets at the time t0 when the first sheet reaches the sheet sensor position. Thereafter, when the transport time Ts for the paper length S elapses, the paper is switched to no paper, and when the transport time Tw for the paper interval W elapses, the paper is switched again to the paper present.

  Although not actually detected, the presence / absence of sheets at the A position, B position, and C position is switched with a delay of the conveyance time Ta, Tb, Tc from the switching of the output of the sheet sensor 52. Therefore, in the illustrated example, the states distinguished by the combination of the presence or absence of paper at the three roller positions are [1], [2], [3], [4], [3], [5], [3]. ], [2], [3],...

  As shown in the middle graph of FIG. 7, the drive current value I of the motor 40 increases and decreases with the state transition. The hatched portion in the graph is an increase in the load accompanying the change with time, and the alternate long and short dash line indicates the initial load at which no change with time has occurred. Here, it is assumed that an increase in load accompanying a change with time is substantially uniform among the three roller positions. Therefore, compared to the state [1] in which paper is present only at one roller position (position A), the load increase in the states [2], [4] and [5] where paper is present at two roller positions. Is doubled. Further, the increase in load in the state [3] in which paper is present at the three roller positions is three times.

  When setting the threshold value Ith, the drive current value I is measured using an image forming apparatus in a condition where the change of the transport mechanism has progressed to the extent that the increase in load at each roller position reaches the upper limit of the allowable range. Then, the drive current value I in the states [2], [4], and [5] where the sheet exists at the (n−1) roller positions is set to the threshold value Ith. By setting the threshold value Ith in this manner, it is possible to detect the condition as an abnormality at a stage where the change over time has evolved until it exceeds the upper limit of the allowable range, and the maintenance work is performed at an appropriate timing. be able to.

  When the set threshold value Ith is applied to binarize the drive current value I, a load determination signal that transitions as shown in the timing chart at the bottom of FIG. 7 is obtained. A high load period in which the drive current value I exceeds the threshold value Ith in the period from the time point ts at which the drive current value I exceeds the threshold value Ith to the time point te when the transport time Ts and the transport time Tw are combined. T1 and the low load period T2 in which the drive current value I is equal to or less than the threshold value Ith appear alternately. As described above, the threshold Ith is the driving current value I in the state [2], [4], [5] where the sheet exists at the (n−1) roller positions, and thus the high load period T1 includes n rollers. This corresponds to state [3] in which a sheet exists at the position. This means that it is not abnormal when only the state [3] corresponds to the high load period T1, and it is abnormal when a state other than the state [3] corresponds to the high load period T1.

  FIG. 8 shows the transition of the drive current value I of the motor 40 when the paper is normally conveyed. When the conveyance is normal, the increase in load due to the change with time is within an allowable range. Therefore, the drive current value I exceeds the threshold value Ith only in the state [3]. The change pattern of the load determination signal is the same as the pattern when the threshold is set in FIG.

  FIG. 9 shows the transition of the drive current value I when the conveyance by the A roller is abnormal. If the conveyance is normal, the condition where the drive current value I changes as indicated by the alternate long and short dash line, and if there is a defect in the A roller or the corresponding drive transmission system, the tolerance is set when a sheet is present at the A position. The increase in load that greatly exceeds is included in the drive current value I. For this reason, after the time ts when the drive current value I first exceeds the threshold value Ith, only the state [4] in which no sheet exists at the A position corresponds to the low load period T2. Note that the transition of the load determination signal indicated by the two-dot chain line in FIG. 9 is the transition when the conveyance is normal.

  The elapsed time Tx from the time t0 when the leading edge of the sheet passes the sheet sensor position to the leading edge of the low load period T2 is the sum of the conveying time Ta corresponding to the A position and the conveying time Ts corresponding to the sheet length S. From this, by measuring the elapsed time Tx, it can be determined that the low load period T2 corresponds to the state [4], that is, that the abnormal location is the A position.

  FIG. 10 shows the transition of the drive current value I when the conveyance by the B roller is abnormal. If there is a problem with the B roller or the corresponding drive transmission system, the drive current value I includes an increase in load that greatly exceeds the allowable range when a sheet is present at the B position. For this reason, after the time ts when the drive current value I first exceeds the threshold value Ith, only the state [5] in which no sheet exists at the B position corresponds to the low load period T2.

  The elapsed time Tx from the time t0 when the leading edge of the sheet passes the sheet sensor position to the leading edge of the low load period T2 is the sum of the conveying time Tb corresponding to the B position and the conveying time Ts corresponding to the sheet length S. From this, by measuring the elapsed time Tx, it is possible to determine that the low load period T2 corresponds to the state [5], that is, that the abnormal part is the B position.

  FIG. 11 shows the transition of the drive current value I when the conveyance by the C roller is abnormal. If there is a defect in the C roller or the corresponding drive transmission system, the drive current value I includes an increase in load that greatly exceeds the allowable range when a sheet is present at the C position. For this reason, after the time ts when the drive current value I first exceeds the threshold value Ith, only the state [2] in which no sheet exists at the C position corresponds to the low load period T2.

  The elapsed time Tx from the time t0 when the leading edge of the sheet passes the sheet sensor position to the leading edge of the low load period T2 is the sum of the conveying time Tc corresponding to the C position and the conveying time Ts corresponding to the sheet length S. From this, by measuring the elapsed time Tx, it can be determined that the low load period T2 corresponds to the state [2], that is, that the abnormal part is the C position.

  FIG. 12 shows the transition of the drive current value I when the conveyance by the A roller and the conveyance by the B roller are abnormal. In the example, after the time point ts when the drive current value I first exceeds the threshold value Ith, a state [4] in which no paper exists at the A position and a state [5] in which no paper exists at the B position correspond to the low load period T2. .

  The elapsed time Tx1 from the time t0 when the leading edge of the paper passes the paper sensor position to the time when the load determination signal first becomes the low load level is the sum of the transport time Ta and the transport time Ts. Further, the elapsed time Tx2 from the time point t0 until the load determination signal once becomes a high load level and again becomes a low load level is the sum of the transport time Tb and the transport time Ts. From this, by measuring the elapsed time Tx1, Tx2, it is determined that the low load period T2 corresponds to the state [4] and the state [5], that is, the abnormal part is the A position and the B position. Can do.

  FIG. 13 shows the transition of the drive current value I when the conveyance by the B roller and the conveyance by the C roller are abnormal. In the example, after the time ts when the drive current value I first exceeds the threshold value Ith, a state [5] in which no paper exists at the B position and a state [2] in which no paper exists at the C position correspond to the low load period T2. .

  The elapsed time Tx1 from the time point t0 to the time point when the load determination signal first becomes the low load level is the sum of the transport time Tb and the transport time Ts. Further, the elapsed time Tx2 from the time point t0 until the load determination signal once becomes a high load level and again becomes a low load level is the sum of the transport time Tc and the transport time Ts. From this, by measuring the elapsed times Tx1 and Tx2, it is determined that the low load period T2 corresponds to the state [5] and the state [2], that is, the abnormal part is the B position and the C position. Can do.

  FIG. 14 shows the transition of the drive current value I when the conveyance by the A roller and the conveyance by the C roller are abnormal. In the example, after the time ts when the drive current value I first exceeds the threshold value Ith, a state [4] in which no paper exists at the A position and a state [2] in which no paper exists at the C position correspond to the low load period T2. .

  The elapsed time Tx1 from the time point t0 to the time point when the load determination signal first becomes the low load level is the sum of the transport time Ta and the transport time Ts. Further, the elapsed time Tx2 from the time point t0 until the load determination signal once becomes a high load level and again becomes a low load level is the sum of the transport time Tc and the transport time Ts. From this, by measuring the elapsed time Tx1, Tx2, it is determined that the low load period T2 corresponds to the state [4] and the state [2], that is, the abnormal part is the A position and the C position. Can do.

  FIG. 15 is a flowchart of the conveyance abnormality detection process executed by the image forming apparatus 1.

  The image forming apparatus 1 executes a conveyance abnormality detection process in parallel with the execution of the print job. The conveyance control unit 47 reads the threshold value Ith corresponding to the size and type of paper used for printing from the storage memory 475 into the work area before starting feeding from the paper stacker 26 to the printer engine 25 ( # 20). The conveyance control unit 47 that instructs the motor driver 46 to drive the motor 40 starts measurement of the drive current value I that periodically takes in the output of the current detection circuit 465 (# 21). In parallel with the measurement of the drive current value I, the output of the paper sensor 52 is monitored, and when the output of the paper sensor 52 changes from the absence of paper to the presence of paper, counting of the elapsed time T is started (# 22).

  Each time the output of the current detection circuit 465 is captured, the measured drive current value I is compared with the threshold value Ith (# 23). When the drive current value I exceeds the threshold value Ith (YES in # 23), it is determined that the load on the motor 40 is at a high level (# 24), and processing for measuring the length of the high load period T1 is performed ( # 25). For example, when a time counter is used for measurement, the counter is started if the counter is not started, and the count is updated when the counter is already started. Then, the counting of the set time Tsw, which is a time obtained by adding the transport time ts and the transport time tw, is started (# 26).

  On the other hand, if the drive current value I does not exceed the threshold value Ith (NO in # 23), it is determined that the load on the motor 40 is at a low level (# 27), and the length of the low load period T2 is measured (# 28). ). Then, the elapsed time T during the time when the load changes from the high level to the low level is stored as the time Tx for specifying the abnormal part (# 29).

  It is checked whether or not the set time Tsw has been timed (# 30), and the processing from step # 23 to step # 29 is repeated until the set time Tsw has been timed. When the measurement of the set time Tsw is completed (YES in # 30), the load height ratio (Duty) is calculated (# 31). The high / low ratio is a ratio of the lengths of the high load period T1 and the low load period T2 measured during the measurement of the set time Tsw.

  If the calculated height ratio R matches the normal height ratio determined when setting the threshold (YES in # 32), the transport mechanism is normal. In this case, the conveyance control unit 47 finishes the conveyance abnormality detection process. On the other hand, if the calculated height ratio R does not match the normal height ratio (NO in # 32), the transport mechanism is abnormal. In this case, the conveyance control unit 47 executes the routine for identifying the abnormal part (# 33).

FIG. 16 is a flowchart of a routine for identifying an abnormal part in the conveyance abnormality detection process. The conveyance control unit 47 specifies the number m of abnormal roller positions (abnormal places) based on the load height ratio R (# 331). At this time, the following equation representing the number m of abnormal roller positions is applied.
m = [(S + W) / W] × R (where S: paper length, W: paper interval, R: height ratio)
Subsequently, transport times Ta, Tb, Tc from the paper sensor position to each roller position are acquired (# 332). As a form of acquisition, it may be calculated from the distances Da, Db, Dc and the conveyance speed V, or previously calculated conveyance times Ta, Tb, Tc may be read from the control data table.

  The abnormal roller position is specified by comparing the previously stored time Tx with the acquired transport times Ta, Tb, and Tc (# 333). Since the number m of abnormal roller positions is specified first, if m abnormal roller positions are specified, the comparison process for specification can be terminated at that time.

  Then, abnormality detection information indicating the specified abnormal roller position is output (# 334). As output forms, there are data transmission to the service center by network communication and display on the display 215 of the operation panel 21.

  In the above embodiment, the functional configuration, hardware configuration, operation, and the like of the image forming apparatus 1 are not limited to examples, and may be changed as appropriate within the scope of the present invention. The number N of rollers may be two or more. An abnormality of the transport mechanism may be detected every time a print job is executed, or may be detected at a predetermined time determined by the cumulative number of printed sheets and the cumulative usage time. Anomalies can be detected by conveying only one sheet.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus P, P1, P2, P3 Paper 50 Conveyance path 41, 42, 43 Roller 40 Motor 52 Paper sensor I Drive current value Ith Threshold 475 Memory 47 Conveyance control part Tx Time S Paper length W Paper interval T1 High load period T2 Low load period

Claims (5)

An image forming apparatus for printing an image on paper,
N (N is an integer greater than or equal to 2) transport rollers disposed at intervals on a transport path through which the paper passes;
A motor that is a common drive source for the N rollers;
A paper sensor for detecting the presence or absence of paper at a detection position upstream of the position where the N rollers on the conveyance path are disposed;
A memory for storing a threshold for determining whether the paper is conveyed correctly based on a driving current value of the motor;
Means for monitoring the transition of the drive current value of the motor during conveyance;
Means for measuring the length of a period from the time when the presence of the paper is detected by the paper sensor to the time when the drive current value exceeds the threshold and then becomes equal to or less than the threshold;
Means for identifying a roller involved in an abnormality among the N rollers, based on a transport time from the detection position to the arrangement position of each of the N rollers and a length of the measured period;
An image forming apparatus comprising: means for outputting abnormality notification information indicating the identified roller. The threshold is one (n−1) rollers less than the maximum number n of rollers that the paper can contact at the same time among the N rollers in a state where the paper is normally conveyed. The image forming apparatus according to claim 1, wherein the driving current value of the motor is when the sheet abuts. The driving current value in a period from the time when the driving current value exceeds the threshold until the conveyance time for a distance including the length in the conveyance direction of the sheet and the sheet interval in the case of continuous sheet passing elapses. Means for timing the length of the low load period in which is less than or equal to the threshold;
2. The apparatus according to claim 1, further comprising: a means for specifying a number of rollers involved in a conveyance abnormality among the N rollers based on the measured length of the low load period and a conveyance time corresponding to the sheet interval. Or the image forming apparatus according to 2; The memory stores a plurality of numerical values determined by the paper type classified by the thickness of the sheet usable as the paper,
The image forming apparatus according to claim 1, wherein a numerical value corresponding to a paper type of the paper among the plurality of stored numerical values is used as the threshold value. The driving current value exceeds the threshold value during a period from when the driving current value exceeds the threshold value until a conveying time corresponding to a distance obtained by combining the length in the paper conveying direction and the paper interval elapses. Means for calculating a ratio between the length of the high load period and the length of the low load period;
The image forming apparatus according to claim 3, wherein the conveyance time closest to the measured length of the period is determined only when the calculated ratio is different from a predetermined normal ratio.

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