Image forming apparatus

Abstract

To provide an image forming apparatus that can detect whether or not foreign matter is attached to an optical rotary encoder while minimizing a decrease in user convenience. [Solution] The image forming apparatus comprises an optical rotary encoder, a DC motor, and a control unit. The optical rotary encoder has a code wheel. The DC motor is to which the optical rotary encoder is attached. The control unit controls the DC motor. The control unit also acquires target speed information indicating a target speed corresponding to the rotational speed of the DC motor, and detects whether or not foreign matter is attached to the code wheel based on the acquired target speed information.

Description

Technical Field

[0001] Embodiments of the present invention relate to an image forming apparatus.

Background Art

[0002] Conventionally, an image forming apparatus provided with an optical rotary encoder has been known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in an image forming apparatus as described in Patent Document 1, when foreign matter adheres during the manufacturing process, the foreign matter is detected in the inspection process. However, the detection of foreign matter in such an inspection process is a means for the manufacturing process, and it is not possible to detect foreign matter adhering to the optical rotary encoder during use of the image forming apparatus by the user. On the other hand, a method of operating the image forming apparatus in a foreign matter detection mode for detecting whether or not foreign matter adheres to the optical rotary encoder has a problem that printing cannot be performed during the execution of the foreign matter detection mode. This leads to a decrease in user convenience, which is not desirable.

[0005] The problem to be solved by the present invention is to provide an image forming apparatus capable of detecting whether or not foreign matter adheres to an optical rotary encoder while suppressing a decrease in user convenience.

Means for Solving the Problems

[0006] The image forming apparatus of this embodiment includes an optical rotary encoder, a DC motor, and a control unit. The optical rotary encoder has a code wheel. The DC motor is to which the optical rotary encoder is attached. The control unit controls the DC motor. The control unit also acquires target speed information indicating a target speed corresponding to the rotational speed of the DC motor, and detects whether or not foreign matter is attached to the code wheel based on the acquired target speed information. [Brief explanation of the drawing]

[0007] [Figure 1] This is an external view showing an example of the overall configuration of the image forming apparatus 100 of the embodiment. [Figure 2] This figure shows an example of a DC motor provided in the image forming apparatus 100. [Figure 3] Figure 2 is an enlarged top view of the code wheel H shown in Figure 2. [Figure 4] This figure shows an example of a pulse signal. [Figure 5] This figure shows an example of a code wheel H with foreign matter attached so large that it completely covers the foreign matter attachment slit. [Figure 6] Figure 5 shows an example of a pulse signal when object OA is attached to the foreign matter attachment slit. [Figure 7] This figure shows an example of a code wheel H with small foreign objects attached to it, enough to cover a portion of the foreign object attachment slit. [Figure 8] Figure 7 shows an example of a pulse signal when object OB is attached to the foreign matter attachment slit. [Figure 9] This figure shows an example of the functional configuration of the image forming apparatus 100. [Figure 10] This figure shows an example of the process flow for the image forming apparatus 100 to calculate the judgment threshold. [Figure 11] This figure shows an example of the process flow for the image forming apparatus 100 to detect whether or not foreign matter is attached to the optical rotary encoder E. [Figure 12]This diagram illustrates the speed stabilization section. The horizontal axis of the graph shown in Figure 12 represents elapsed time. [Modes for carrying out the invention]

[0008] The image forming apparatus of the embodiment will be described with reference to the drawings. In each figure, the same components are denoted by the same reference numerals. As an example of the image forming apparatus of the embodiment, the image forming apparatus 100 will be described as an example.

[0009] (Details of the image forming apparatus) Refer to Figure 1 for a detailed explanation of the image forming apparatus 100.

[0010] Figure 1 is an external view showing an example of the overall configuration of an image forming apparatus 100 according to an embodiment. The image forming apparatus 100 can be any apparatus that is equipped with various DC motors and capable of forming an image on a printing medium. In the example shown in Figure 1, the image forming apparatus 100 is a multifunction device that performs image processing such as scanning and faxing (facsimile) in addition to forming an image on a printing medium, but is not limited to this. Image processing refers to processing related to images. Image processing includes, for example, the process of reading image information to be read, the process of recording (storing) image information, and the process of transmitting the image to another device. The printing medium can be any sheet-like medium, such as printing paper or sticker paper, but is not limited to these.

[0011] The image forming apparatus 100 includes a display 110, a control panel 120, a printer unit 130, a print media storage unit 140, and an image reading unit 150. The printer unit 130 of the image forming apparatus 100 may be a device for fixing toner images, or it may be an inkjet type device.

[0012] The image forming apparatus 100 generates digital data by reading an image appearing on a reading target and generates an image file. The reading target may be any medium as long as it is a sheet-like medium, for example, paper on which a document, characters, an image, etc. are described.

[0013] The display 110 is an image display device such as a liquid crystal display or an organic EL (Electro Luminescence) display. The display 110 displays various information regarding the image forming apparatus 100.

[0014] The control panel 120 has a plurality of buttons. The control panel 120 receives user operations. The control panel 120 outputs a signal corresponding to the operation performed by the user to the control unit of the image forming apparatus 100. The display 110 and the control panel 120 may be configured as an integrated touch panel.

[0015] The printer unit 130 forms an image on a printing medium based on the image information generated by the image reading unit 150 or the image information received via a communication path. The printer unit 130 forms an image by, for example, the following processing. The image forming unit of the printer unit 130 forms an electrostatic latent image on a photoreceptor drum based on the image information. The image forming unit of the printer unit 130 forms a visible image by attaching a developer to the electrostatic latent image. A specific example of the developer is toner. The transfer unit of the printer unit 130 transfers the visible image onto the printing medium. The fixing unit of the printer unit 130 fixes the visible image onto the printing medium by heating and pressurizing the printing medium.

[0016] The printing medium storage unit 140 stores the printing medium used for image formation in the printer unit 130.

[0017] The image reading unit 150 reads the image information of the reading target as the brightness and darkness of light. The image reading unit 150 records the read image information. The recorded image information may be transmitted to other information processing apparatuses via a network. The recorded image information may be formed as an image on a print medium by the printer unit 130.

[0018] The image forming apparatus 100 having such a configuration includes various DC motors inside the printer unit 130 and the image reading unit 150 respectively. The DC motors included in the image forming apparatus 100 may be, for example, a DC motor that rotates a conveyance roller that conveys a print medium inside the printer unit 130, a DC motor that moves other movable parts inside the printer unit 130, and the like. The DC motors included in the image forming apparatus 100 may be, for example, a DC motor that rotates a roller that conveys a reading target inside the image reading unit 150, a DC motor that moves other movable parts inside the image reading unit 150, and the like. FIG. 2 is a diagram showing an example of the DC motor included in the image forming apparatus 100. The DC motor M shown in FIG. 2 is an example of the DC motor included in the image forming apparatus 100. As an example, a case where the DC motor M is a conveyance motor that rotates a conveyance roller that conveys a print medium inside the printer unit 130 will be described.

[0019] The DC motor M is, for example, a servo motor that operates with DC power, but instead, it may be other motors that operate with DC power. An optical rotary encoder E is attached to the DC motor M. A gear G is attached to the rotation shaft of the DC motor M. The DC motor M transmits a driving force to the conveyance roller via a gear train or the like that meshes with the gear G.

[0020] The optical rotary encoder E has a code wheel H and a transmissive sensor S.

[0021] The code wheel H is a disc-shaped scale. Figure 3 is an enlarged top view of the code wheel H shown in Figure 2. As shown in Figure 3, the code wheel H has markings called slits. In Figure 3, each of the multiple slits formed on the code wheel H is indicated by a black rectangle. Slit SL shown in Figure 3 is one of these multiple slits. The code wheel H is mounted on the rotating shaft of the DC motor M so as to rotate coaxially with the rotating shaft of the DC motor M in accordance with the rotation of the motor's rotating shaft.

[0022] The transmissive sensor S sandwiches the code wheel H between a light-emitting element and a light-receiving element, and the light-receiving element detects whether or not the light emitted from the light-emitting element passes through the slit of the code wheel. The transmissive sensor S outputs an L-level signal when the light emitted from the light-emitting element passes through the slit of the code wheel H and is received by the light-receiving element. On the other hand, the transmissive sensor S outputs an H-level signal when the light emitted from the light-emitting element does not pass through the slit of the code wheel H, that is, when the light is not received by the light-receiving element. For this reason, the transmissive sensor S outputs a pulse signal corresponding to the rotation of the code wheel H. For the sake of explanation, the pulse signal output from the transmissive sensor S will be simply referred to as the pulse signal. For the sake of explanation, the width of the pulses contained in the pulse signal will be referred to as the pulse width of the pulse signal. The pulse width of the pulse signal is determined according to the rotational speed of the code wheel H, that is, the rotational speed of the DC motor M. In other words, the pulse width of the pulse signal corresponds one-to-one with the rotational speed of the DC motor M. Therefore, the image forming apparatus 100 can determine the pulse width of the pulse signal based on the rotational speed of the DC motor M.

[0023] Figure 4 shows an example of a pulse signal. The horizontal axis of the graph in Figure 4 represents elapsed time. The vertical axis of the graph represents the level of the pulse signal. In Figure 4, this level is indicated by "Encoder Output Level (H / L)". Figure 4 shows the pulses included in the pulse signal that are output from the transmissive sensor S during one rotation of the rotation axis of the DC motor M. The time tA shown in Figure 4 is the pulse width of the pulse signal shown in Figure 4. For the sake of explanation, the rotational speed of the DC motor M will be simply referred to as rotational speed. For the sake of explanation, the rotational speed when the pulse width is expressed by time tA will be referred to as rotational speed V.

[0024] As shown above, the pulse width of the pulse signal may change if foreign matter adheres to the code wheel H. For example, as shown in Figure 5, if foreign matter adheres to the code wheel H in such a way that it covers one of the slits of the code wheel H, the through-sensor S will output a pulse signal as shown in Figure 6. For the sake of explanation, the slit of the code wheel H to which foreign matter adheres will be referred to as the foreign matter-attached slit. Figure 5 is a diagram showing an example of the state of the code wheel H when a large piece of foreign matter adheres to it, enough to cover the foreign matter-attached slit. Figure 6 is a diagram showing an example of a pulse signal when object OA adheres to the foreign matter-attached slit as shown in Figure 5. Object OA shown in Figure 5 is an example of foreign matter adhered to the foreign matter-attached slit. The horizontal axis of the graph shown in Figure 6 represents elapsed time. The vertical axis of the graph, like the vertical axis of the graph shown in Figure 4, represents the pulse signal level. However, in the example shown in Figure 6, the rotational speed of the DC motor M is rotational speed V.

[0025] As shown in Figure 5, when an object OA is attached to the foreign matter attachment slit, the through-beam sensor S periodically outputs a pulse with a pulse width of time tA and a pulse with a pulse width of time tB. This is because, as shown in Figure 5, when the foreign matter attachment slit is covered by object OA, the light emitted from the light-emitting part of the through-beam sensor S does not pass through the foreign matter attachment slit. If the light does not pass through the foreign matter attachment slit, the light is not received by the light-receiving part until the next slit after the foreign matter attachment slit passes between the light-emitting part and the light-receiving part. Therefore, in this case, time tB becomes twice time tA. That is, tB = tA * 2. In this embodiment, * indicates multiplication. This means that it is possible to detect whether or not foreign matter is attached to the code wheel H by whether or not a pulse with a pulse width of twice or more than the pulse width corresponding to the rotation speed appears in the pulse signal. More specifically, the image forming apparatus 100 can determine that, when the pulse appears in the pulse signal, a foreign object large enough to cover the foreign object attachment slit has adhered to the code wheel H.

[0026] On the other hand, for example, if foreign matter adheres to the code wheel H in such a way that it covers a portion of the foreign matter adhesion slit, as shown in Figure 7, the through-sensor S tends to output a pulse signal as shown in Figure 8. Figure 7 is a diagram showing an example of the state of the code wheel H with small foreign matter adhering to it that covers a portion of the foreign matter adhesion slit. Figure 8 is a diagram showing an example of a pulse signal when object OB is adhering to the foreign matter adhesion slit as shown in Figure 7. Object OB shown in Figure 7 is an example of foreign matter that covers a portion of the foreign matter adhesion slit. The horizontal axis of the graph shown in Figure 8 represents elapsed time. The vertical axis of the graph represents the pulse signal level, similar to the vertical axis of the graph shown in Figure 4. However, in the example shown in Figure 8, the rotational speed is rotational speed V.

[0027] As shown in Figure 7, when an object OB is attached to the foreign matter attachment slit, the transmissive sensor S periodically outputs a pulse with a pulse width of time tA and a pulse with a pulse width of time tC. This is because, as shown in Figure 7, when a part of the foreign matter attachment slit is covered by object OB, the light emitted from the light-emitting part of the transmissive sensor S passes through a part of the foreign matter attachment slit but not the other part. Here, if the size of the foreign matter covering a part of the foreign matter attachment slit is greater than (1 / 2) times the width of the foreign matter attachment slit, the pulse signal may become a pulse signal as shown in Figure 6. This is because, in this case, the light emitted from the light-emitting part has difficulty passing through the foreign matter attachment slit. Therefore, in this case, the image forming apparatus 100 can detect whether or not foreign matter is attached to the code wheel H by checking whether or not pulses with a pulse width of twice or more corresponding to the rotation speed appear in the pulse signal. On the other hand, if the size of the foreign matter covering a part of the foreign matter attachment slit is (1 / 2) times the width of the foreign matter attachment slit, the pulse signal becomes a pulse signal as shown in Figure 7. Time tC is (1 / 2) times time tA. That is, tC = tA * (1 / 2). This means that it is possible to detect whether or not foreign matter is attached to the code wheel H by whether or not a pulse with a pulse width of (1 / 2) times or less of the pulse width corresponding to the rotation speed appears in the pulse signal. This is because if the size of the foreign matter covering a part of the foreign matter attachment slit is less than (1 / 2) times the width of the foreign matter attachment slit, the smallest pulse width that appears in the pulse signal will be less than (1 / 2) times time tA. Therefore, the image forming apparatus 100 can determine that a small foreign matter, enough to cover a part of the foreign matter attachment slit, is attached to the code wheel H if a pulse with a pulse width of (1 / 2) times or less of the pulse width corresponding to the rotation speed appears in the pulse signal.

[0028] From the above, the image forming apparatus 100 can determine whether or not foreign matter is attached to the code wheel H based on the pulse signal. To achieve this, the image forming apparatus 100 acquires target speed information indicating a target speed for a speed corresponding to the rotation speed, and detects whether or not foreign matter is attached to the code wheel H based on the acquired target speed information. More specifically, the image forming apparatus 100 calculates a threshold for the pulse width of the pulse signal based on the acquired target speed information, and detects whether or not foreign matter is attached to the code wheel H based on the calculated threshold. The aforementioned times tB and tC are examples of such thresholds. As a result, the image forming apparatus 100 can determine whether or not foreign matter is attached to the optical rotary encoder E without stopping various processes performed by the user, even during normal use by the user. In other words, the image forming apparatus 100 can detect whether or not foreign matter is attached to the optical rotary encoder E while suppressing a decrease in user convenience.

[0029] (Functional configuration of an image forming apparatus) Referring to Figure 9, the functional configuration of the image forming apparatus 100 will be described.

[0030] Figure 9 shows an example of the functional configuration of the image forming apparatus 100.

[0031] The image forming apparatus 100 includes a display 110, a control panel 120, a printer unit 130, a print media storage unit 140, and an image reading unit 150. The image forming apparatus 100 also includes a control unit 300, a network interface 310, a storage unit 320, and a memory 330. These functional units of the image forming apparatus 100 are communicated together via a system bus.

[0032] The display 110, control panel 120, printer unit 130, print media storage unit 140, and image reading unit 150 will be described in the same way as above, so their descriptions will be omitted. The control unit 300, network interface 310, storage unit 320, and memory 330 will be described below.

[0033] The control unit 300 is an example of a control unit for the image forming apparatus 100. The control unit 300 is configured to include the CPU (Central Processing Unit) of the image forming apparatus 100. The control unit 300 controls the operation of each functional part of the image forming apparatus 100. The control unit 300 performs various processes by executing a program. The control unit 300 obtains instructions entered by the user from the control panel 120. That is, the control unit 300 accepts operations from the user via the control panel 120. The control unit 300 performs control processing based on the obtained instructions. The control unit 300 may also include other processors such as FPGA (Field Programmable Gate Array) instead of the CPU.

[0034] The network interface 310 transmits and receives data with other devices. It operates as an input interface, receiving data transmitted from other devices. It also operates as an output interface, transmitting data to other devices.

[0035] The memory unit 320 is, for example, an auxiliary storage device such as a hard disk or an SSD (Solid State Drive). The memory unit 320 stores various types of information. For example, the memory unit 320 stores programs executed by the control unit 300. These programs are, for example, firmware or applications.

[0036] Memory 330 is, for example, RAM (Random Access Memory). Memory 330 temporarily stores information used by each functional unit of the image forming apparatus 100. Memory 330 may store image information read by the image reading unit 150, programs for operating each functional unit, and the like.

[0037] (A process in which the image forming apparatus calculates a threshold value to detect whether or not foreign matter is attached to the optical rotary encoder.) Referring to Figure 10, the process by which the image forming apparatus 100 calculates a threshold for detecting whether or not foreign matter is attached to the optical rotary encoder E will be described. For the sake of explanation, the threshold for detecting whether or not foreign matter is attached to the optical rotary encoder E will be simply referred to as the judgment threshold. Figure 10 is a diagram showing an example of the process flow for which the image forming apparatus 100 calculates the judgment threshold. That is, Figure 10 shows an example of the process flow executed by the image forming apparatus 100 for the DC motor M. The process of the flowchart shown in Figure 10 may be applied to at least some of the DC motors other than DC motor M among the DC motors provided by the image forming apparatus 100. For example, when the power of the image forming apparatus 100 is turned on, the image forming apparatus 100 continues to execute the process of the flowchart shown in Figure 10 until the power of the image forming apparatus 100 is turned off.

[0038] The control unit 300 waits until it acquires target speed information indicating a target speed corresponding to the rotational speed (ACT110). This speed may be the rotational speed itself, the transport speed of the printing medium transported according to the rotation of the DC motor M, or any other speed corresponding to the rotation of the DC motor M. As an example, the case where this speed is the rotational speed itself will be described. When the control unit 300 acquires the target speed information, it starts rotating the DC motor M through a process different from the flowchart shown in Figure 11, and starts feedback control of the DC motor M to bring the rotational speed closer to the rotational speed indicated by the target speed information.

[0039] When the control unit 300 determines that it has acquired target speed information (ACT110-YES), it identifies a pulse width corresponding to the target speed indicated by the acquired target speed information as the pulse width of the pulse signal (ACT120). The aforementioned time tA is an example of a pulse width corresponding to the target speed when the target speed is the rotational speed V. For the sake of explanation, the pulse width calculated in ACT120 will be referred to as the target pulse width. For example, the control unit 300 may be configured to perform the processing of ACT120 based on a function that calculates a pulse width corresponding to the target speed by substituting the target speed. For example, the control unit 300 may be configured to perform the processing of ACT120 based on correspondence information that associates the target speed with the pulse width corresponding to the target speed. In this case, the correspondence information is stored in advance in the storage unit 320. The control unit 300 may be configured to perform the processing of ACT120 by other methods.

[0040] Next, the control unit 300 calculates a judgment threshold based on the target pulse width (ACT130). Specifically, in ACT130, the control unit 300 calculates a pulse width twice the target pulse width as the first threshold. The first threshold is the threshold for detecting foreign objects larger than the slit width of the code wheel H. On the other hand, in ACT130, the control unit 300 calculates a pulse width (1 / 2) times the target pulse width as the second threshold. The second threshold is the threshold for detecting foreign objects smaller than the slit width of the code wheel H. In other words, the judgment threshold calculated by the control unit 300 in ACT130 includes these two thresholds: the first threshold and the second threshold. The aforementioned time tB is an example of the first threshold. The aforementioned time tC is an example of the second threshold.

[0041] Next, the control unit 300 stores threshold information representing each of the two thresholds calculated as judgment thresholds in ACT130 in the storage unit 320 (ACT140). After the processing of ACT140 is completed, the control unit 300 transitions to ACT110 and waits again until it acquires target speed information indicating the target speed for the speed corresponding to the rotation speed. That is, the image forming apparatus 100 calculates a judgment threshold each time it acquires target speed information. Here, as mentioned above, the rotation speed corresponds one-to-one with the pulse width of the pulse signal. For this reason, the image forming apparatus 100 calculates different thresholds depending on whether it acquires target speed information indicating a first target speed or target speed information indicating a second target speed. However, the second target speed is a different target speed from the first target speed.

[0042] The control unit 300 may be configured to perform ACT120 or lower processing if it determines that it has acquired target speed information in the ACT110 process described above, and if the target speed indicated by the acquired target speed information has changed. In this case, the control unit 300 calculates a determination threshold each time the target speed indicated by the acquired target speed information changes.

[0043] As described above, when the image forming apparatus 100 acquires target speed information, it can calculate a judgment threshold based on the acquired target speed information. As a result, the image forming apparatus 100 can detect whether or not foreign matter is attached to the code wheel H based on the calculated judgment threshold.

[0044] (A process in which an image forming apparatus detects whether or not foreign matter is attached to the optical rotary encoder.) Referring to Figure 11, the process by which the image forming apparatus 100 detects whether or not foreign matter is attached to the optical rotary encoder E will be described. Figure 11 is a diagram showing an example of the flow of the process by which the image forming apparatus 100 detects whether or not foreign matter is attached to the optical rotary encoder E. The process of the flowchart shown in Figure 11 may be applied to at least some of the DC motors other than DC motor M among the DC motors provided in the image forming apparatus 100. For example, when the power of the image forming apparatus 100 is turned on, the process of the flowchart shown in Figure 11 will continue to be executed until the power of the image forming apparatus 100 is turned off.

[0045] The control unit 300 waits until the DC motor M starts rotating (ACT210). In Figure 11, the process of ACT110 is indicated by "Motor rotation start?". The method by which the control unit 300 performs the process of ACT210 may be a known method or a method to be developed in the future.

[0046] When the control unit 300 determines that the DC motor M has started rotating (ACT210-YES), it begins acquiring pulse signals from the transmissive sensor S and waits until the rotation speed stabilizes based on the acquired pulse signals (ACT220). This means that the control unit 300 executes the processing from ACT230 onward within the speed stabilization section. Figure 12 is a diagram illustrating the speed stabilization section. The horizontal axis of the graph shown in Figure 12 represents elapsed time. The vertical axis of the graph represents the frequency of the pulse signal. In Figure 12, the frequency of the pulse signal is shown as the "encoder frequency". When the control unit 300 attempts to rotate the DC motor M so that the rotation speed matches the target speed, the frequency of the pulse signal changes over time, for example, along the curve shown in Figure 12. That is, in the section PA at the beginning of the DC motor M's rotation, the frequency of the pulse signal overshoots. This is because, in section PA, the rotation speed temporarily exceeds the target speed due to the feedback control of the DC motor M. Even if a change occurs in the pulse width of the pulse signal in section PA, it is difficult to distinguish this change from a change due to overshoot. On the other hand, after section PA, the rotation speed stabilizes. That is, the section indicated by "speed stable section" in Figure 12 is the section in which the rotation speed is stable, excluding fluctuations due to noise, vibration, etc. If the pulse width of the pulse signal changes in the speed stable section, the control unit 300 can accurately detect that the pulse width of the pulse signal has changed. In Figure 12, the change in the frequency of the pulse signal in response to such a change in the pulse width of the pulse signal is shown by the drop in the frequency of the pulse signal within the speed stable section. This speed stable section continues until the rotation of the DC motor M stops. Therefore, the control unit 300 determines whether or not foreign matter is attached to the optical rotary encoder E between the time after section PA and the time the rotation of the DC motor M stops. The method by which the control unit 300 determines whether or not the rotation speed is stable is, for example, by determining whether or not the frequency of the pulse signal acquired by the control unit 300 has not changed for a predetermined time or longer, but it is not limited to this method.

[0047] When the control unit 300 determines that the rotation speed has stabilized (ACT220-YES), it determines whether or not foreign matter is attached to the optical rotary encoder E based on the acquired pulse signal (ACT230). The process of ACT230 will be explained below.

[0048] The control unit 300 executes the following process as the process of ACT230. The control unit 300 reads threshold information from the storage unit 320 that indicates the judgment threshold calculated by the flowchart shown in Figure 10. After reading the threshold information, the control unit 300 makes two determinations in the acquired pulse signal: whether a pulse with a pulse width greater than or equal to the first threshold indicated by the read threshold information has appeared, and whether a pulse with a pulse width less than or equal to the second threshold indicated by the read threshold information has appeared. If the control unit 300 determines that a pulse with a pulse width greater than or equal to the first threshold indicated by the read threshold information has appeared, it determines that foreign matter is attached to the optical rotary encoder E. Specifically, in this case, the control unit 300 determines that foreign matter larger than the slit width of the slit of the code wheel H is attached to the code wheel H. On the other hand, if the control unit 300 determines that a pulse with a pulse width less than or equal to the second threshold indicated by the read threshold information has appeared, it also determines that foreign matter is attached to the optical rotary encoder E. Specifically, in this case, the control unit 300 determines that a foreign object smaller than the slit width of the code wheel H is attached to the code wheel H. If the control unit 300 determines that no pulses with a pulse width greater than or equal to the first threshold indicated by the read threshold information have appeared, and also determines that no pulses with a pulse width less than or equal to the second threshold indicated by the read threshold information have appeared, then the control unit 300 determines that no foreign object is attached to the optical rotary encoder E. The control unit 300 executes the above process as the process of ACT230.

[0049] If the control unit 300 determines that no foreign matter is attached to the optical rotary encoder E (ACT230-NO), it determines whether or not the rotation of the DC motor M has stopped (ACT240). The method by which the control unit 300 determines whether or not the rotation of the DC motor M has stopped may be a known method or a method to be developed in the future.

[0050] If the control unit 300 determines that the rotation of the DC motor M has not stopped (ACT240-NO), it transitions to ACT230 and determines again whether or not foreign matter is attached to the optical rotary encoder E.

[0051] On the other hand, if the control unit 300 determines that the rotation of the DC motor M has stopped (ACT240-YES), it transitions to ACT210 and waits again until the DC motor M starts rotating again.

[0052] On the other hand, if it is determined that foreign matter is attached to the optical rotary encoder E (ACT230-YES), error processing is performed (ACT250). Error processing is a process performed by the control unit 300 in response to the presence of foreign matter on the optical rotary encoder E. Error processing may include, for example, a process to notify other devices that foreign matter is attached to the code wheel H. Such other devices may be, but are not limited to, service technicians contracted to maintain the image forming apparatus 100, or PCs (personal computers) of companies, etc. Error processing may include, for example, a process to display information on the display 110 prompting the removal of the foreign matter attached to the code wheel H. Error processing may include, for example, a process to stop the rotation of the DC motor M. Error processing may include, for example, a process to stop the formation of an image on the printing medium. Error processing may include, for example, a process to display information on the display 110 indicating that foreign matter is attached to the optical rotary encoder E. Error handling may include, for example, identifying a slit in the code wheel H that is presumed to have foreign matter attached as a foreign matter-attached slit, and stopping the DC motor M so that the identified foreign matter-attached slit is located at a predetermined position. This predetermined position may be any position that makes it easy for a person cleaning the code wheel H, such as a service technician who is contracted to maintain the image forming apparatus 100, to remove the foreign matter. This predetermined position is, for example, the position opposite the position of the transmissive sensor S across the central axis of the code wheel H, but is not limited to this. Error handling may also include other processes in place of, or in addition to, some or all of, these processes. After the processing of ACT250 is performed, the control unit 300 terminates the processing shown in the flowchart in Figure 11.

[0053] As described above, the image forming apparatus 100 can detect whether or not foreign matter is attached to the code wheel H based on a determination threshold calculated based on target speed information indicating a target speed corresponding to the rotational speed of the DC motor. As a result, the image forming apparatus 100 can determine whether or not foreign matter is attached to the optical rotary encoder E without stopping various processes performed by the user. In other words, the image forming apparatus 100 can detect whether or not foreign matter is attached to the optical rotary encoder E while suppressing a decrease in user convenience.

[0054] The matters described above may be combined in any way. The target speed described above may be replaced, for example, with a target value for the duty cycle of the PWM (Pulse Width Modulation) signal supplied to the DC motor M when controlling the DC motor M using open-loop control. In this case, the image forming apparatus 100, for example, in ACT120, determines the pulse width of the pulse signal based on the target value.

[0055] (Note) [1] An image forming apparatus comprising: an optical rotary encoder having a code wheel; a DC motor to which the optical rotary encoder is attached; and a control unit for controlling the DC motor, wherein the control unit acquires target speed information indicating a target speed corresponding to the rotational speed of the DC motor, and detects whether or not foreign matter is attached to the code wheel based on the acquired target speed information. [2] The control unit calculates a threshold value for the pulse width of the pulse signal output from the optical rotary encoder based on the target speed information, and detects whether or not foreign matter is attached to the code wheel based on the calculated threshold value, as described in [1]. [3] The image forming apparatus according to [2], wherein the threshold includes a first threshold for detecting foreign matter larger than the slit width of the code wheel and a second threshold for detecting foreign matter smaller than the slit width of the code wheel, and the control unit determines that foreign matter larger than the slit width of the code wheel is attached to the code wheel when the pulse width greater than or equal to the first threshold is output from the optical rotary encoder, and determines that foreign matter smaller than the slit width of the code wheel is attached to the code wheel when the pulse width less than or equal to the second threshold is output from the optical rotary encoder. [4] The image forming apparatus according to [2] or [3], wherein the control unit calculates different threshold values ​​depending on whether the target speed information indicating a first target speed is acquired or whether the target speed information indicating a second target speed is acquired. [5] The control unit calculates the threshold value each time the target speed indicated by the acquired target speed information changes, as described in any one of [2] to [4]. [6] The image forming apparatus according to any one of [1] to [5], wherein the control unit detects that foreign matter is attached to the code wheel and performs processing corresponding to the presence of foreign matter on the code wheel. [7] The image forming apparatus according to [6], wherein the process includes a process of notifying other devices that foreign matter is attached to the code wheel. [8] The process includes identifying a slit in the code wheel that is presumed to have foreign matter attached to it as a foreign matter-attached slit, and stopping the DC motor so that the identified foreign matter-attached slit is located at a predetermined position, as described in [6] or [7].

[0056] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0057] A program for realizing the function of any component in the apparatus described above (for example, the image forming apparatus 100) may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Here, "computer system" includes hardware such as the OS (Operating System) and peripheral devices. "Computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, CD (Compact Disk)-ROMs, and storage devices such as hard disks built into a computer system. "Computer-readable recording medium" also includes volatile memory (RAM) inside a computer system that acts as a server or client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line, which holds the program for a certain period of time.

[0058] The above program may be transmitted from a computer system that stores this program in a memory device or the like to another computer system via a transmission medium or by transmission waves within the transmission medium. The "transmission medium" used to transmit the program refers to a medium that has the function of transmitting information, such as a network (communication network) like the Internet or a communication line (communication line) like a telephone line. The above program may be intended to implement some of the functions described above. The above program may also be a so-called differential file (differential program) that can implement the functions described above in combination with a program already recorded in the computer system. [Explanation of symbols]

[0059] 100…Image forming apparatus, 110…Display, 120…Control panel, 130…Printer unit, 140…Print media storage unit, 150…Image reading unit, 300…Control unit, 310…Network interface, 320…Storage unit, 330…Memory, E…Optical rotary encoder, G…Gear, H…Code wheel, M…DC motor, OA, OB…Object, S…Transmissive sensor, SL…Slit

Claims

1. An optical rotary encoder having a code wheel, A DC motor to which the aforementioned optical rotary encoder is attached, A control unit for controlling the DC motor, Equipped with, The control unit acquires target speed information indicating a target speed corresponding to the rotational speed of the DC motor, and detects whether or not foreign matter is attached to the code wheel based on the acquired target speed information. Image forming apparatus.

2. The control unit calculates a threshold value for the pulse width of the pulse signal output from the optical rotary encoder based on the target speed information, and detects whether or not foreign matter is attached to the code wheel based on the calculated threshold value. The image forming apparatus according to claim 1.

3. The threshold includes a first threshold for detecting foreign objects larger than the slit width of the code wheel, and a second threshold for detecting foreign objects smaller than the slit width of the code wheel. The control unit determines that if the pulse width output from the optical rotary encoder is greater than or equal to the first threshold, a foreign object larger than the slit width of the code wheel is attached to the code wheel, and determines that if the pulse width output from the optical rotary encoder is less than or equal to the second threshold, a foreign object smaller than the slit width of the code wheel is attached to the code wheel. The image forming apparatus according to claim 2.

4. The control unit calculates different thresholds depending on whether it has acquired target speed information indicating a first target speed as the target speed or target speed information indicating a second target speed as the target speed. The image forming apparatus according to claim 2.

5. The control unit calculates the threshold value each time the target speed indicated by the acquired target speed information changes. The image forming apparatus according to claim 2.

6. When the control unit detects that foreign matter is attached to the code wheel, it performs processing corresponding to the presence of foreign matter on the code wheel. The image forming apparatus according to claim 1.

7. The process includes notifying other devices that foreign matter is attached to the code wheel. The image forming apparatus according to claim 6.

8. The process includes identifying a slit in the code wheel that is presumed to have foreign matter attached to it as a foreign matter-attached slit, and stopping the DC motor so that the identified foreign matter-attached slit is located at a predetermined position. The image forming apparatus according to claim 6.

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