Motor control device and image reading device

Abstract

To prevent a motor from being overheated without using a cooling fan and a temperature sensor of the motor by calculating a temperature of the motor on the basis of basic characteristics such as a temperature coefficient and electric resistance of a winding of the motor.SOLUTION: An image reading device 10 comprises a control unit 45 that calculates a maximum temperature Tmax of a motor 46, calculates a rising temperature Tj of the motor 46 in operation on the basis of the following formula (B), where a thermal time constant of the motor 46 is taken as τ and Napier's number is taken as e, stops the motor 46 when the rising temperature Tj of the motor 46 exceeds a first temperature threshold TS1, calculates a lowering temperature Tk of the stopped motor 46 on the basis of the following formula (C), and restarts the operation of the motor 46 when the lowering temperature Tk of the motor 46 becomes lower than a second temperature threshold TS2. (B): Tj=Tamb+(Tmax-Tamb)*(1-e-t / τ), (C): Tk=Tamb+(Tmax-Tamb)*e-t / τ.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a motor control device that controls a motor and an image reading device that includes the same, and more particularly to a technique for preventing the motor from overheating. [Background technology]

[0002] For example, in an image reading device, a document is transported by the driving force of a motor, and the image of the document is read using an imaging element such as a CIS (Contact Image Sensor) or a CCD (Charge Coupled Device). However, if the motor is overloaded, it may overheat, so it is necessary to deal with the temperature rise of the motor.

[0003] For example, in the conveying device and recording device described in Patent Document 1, the temperature of the motor or the parts surrounding the motor is predicted by adding or subtracting parameters related to the operating state of the motor and the cumulative number of rotations of the motor within a specified period of time, and based on the value obtained from the temperature prediction, the operating mode is transitioned between normal mode and temperature rise suppression mode to prevent the motor from overheating and overloading. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-155009 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, the temperature of the motor or its surroundings is predicted by adding or subtracting parameters related to the operating state of the motor and the cumulative number of rotations of the motor within a specified time. Therefore, the parameters affect the accuracy of the temperature prediction, and it is necessary to prepare in advance many temperature coefficients and the like as parameters.

[0006] The present invention has been made in consideration of the above circumstances, and aims to enable control to be performed to prevent the motor from overheating by calculating the motor temperature based on basic characteristics such as the electrical resistance and temperature coefficient of the motor windings, without using a cooling fan or motor temperature sensor. [Means for solving the problem]

[0007] A motor control device according to one aspect of the present invention includes a motor, a temperature sensor that detects an ambient temperature of the motor, and a control unit that controls the motor, and when the temperature of the motor is T, a preset reference temperature of the motor is T0, a known electrical resistance of the motor winding at the reference temperature T0 is R0, a temperature coefficient of resistance of the motor winding is α, the ambient temperature of the motor detected by the temperature sensor is Tamb, and the thermal resistance between the motor winding and the ambient space is Rth, and a current supplied to the motor is I, The control unit is configured to th *R0*(1+α*(T-T0))*I 2 +T amb a temperature T of the motor is calculated based on the formula (A), and the calculated temperature T is set as the maximum temperature Tmax of the motor; a thermal time constant of the motor is τ, and the Napier's number is e; while the motor is operating, a rising temperature Tj of the motor that rises with the time t during which the motor is operating is calculated based on the following formula (B); Tj=T amb +(T max -T amb )*(1-e -t / τ) …Formula (B) When the motor is stopped, a falling temperature Tk of the motor, which falls with the time t during which the motor is stopped, is calculated based on the following formula (B): Tk=T amb +(T max -T amb )*e -t / τ...Formula (C) The motor is operated, and when the rising temperature Tj of the motor exceeds a predetermined first temperature threshold TS1, the motor is stopped, and when the falling temperature Tk of the motor becomes less than a predetermined second temperature threshold TS2 that is lower than the first temperature threshold TS1, the operation of the motor is resumed. [Effects of the Invention]

[0008] According to the present invention, the temperature of the motor is calculated based on basic characteristics such as the electrical resistance and temperature coefficient of the motor windings, and control can be performed to prevent the motor from overheating without using a cooling fan or motor temperature sensor. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing an image reading device to which a motor control device according to an embodiment of the present invention is applied; [Figure 2] FIG. 2 is a cross-sectional view showing the appearance of the image reading device. [Figure 3] FIG. 1 is a block diagram illustrating a configuration of an image reading device. [Figure 4] 1 is a graph showing the characteristics of the temperature rise of a motor. [Figure 5] 10 is a graph showing the characteristics of the falling temperature of a motor. [Figure 6] 10 is a graph showing the temperature change of a motor due to operation or stoppage. [Figure 7] 10 is a flowchart showing a control procedure for a motor. DETAILED DESCRIPTION OF THE INVENTION

[0010] A motor control device according to one embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a cross-sectional view showing an image reading device to which a motor control device according to one embodiment of the present invention is applied. Fig. 2 is a perspective view showing the appearance of the image reading device, showing a state in which a document transport unit 21 is open.

[0011] 1 and 2, the image reading device 10 includes a document transport unit 21 and a reading unit 22. The document transport unit 21 is a so-called automatic document feeder, and includes a document tray 23, a paper feed roller 24, a registration roller 25, a plurality of transport rollers 26, a paper discharge roller 27, and a document discharge tray 28. The reading unit 22 includes a first platen glass 31, a second platen glass 32, a carriage 34, an optical system unit 35, a condenser lens 36, and a CCD sensor 37.

[0012] In the reading unit 22, the carriage 34 includes a light source 34A that irradiates the document with light and a mirror 34B that reflects the light reflected by the document M.

[0013] The optical system unit 35 includes a mirror 35A and a mirror 35B. The mirror 35A receives light reflected by the mirror 34B of the carriage 34 and redirects the light substantially vertically downward. The mirror 35B further redirects the light reflected by the mirror 35A substantially horizontally and guides it to the CCD sensor 37 via the condenser lens 36.

[0014] The carriage 34 and the optical system unit 35 are arranged to be movable back and forth along rails in a sub-scanning direction X perpendicular to the main scanning direction Y, and are moved in the sub-scanning direction X while maintaining a predetermined speed relationship by a known drive mechanism powered by a stepping motor (not shown).

[0015] Two hinges 29 are provided at a distance from one end of the upper surface 22a of the reading unit 22, and these hinges 29 support the document transport unit 21 so that it can be opened and closed, allowing the user to open and close the document transport unit 21.

[0016] Here, the image reading device 10 can switch between a first mode in which an image of the original M placed on the second platen glass 32 is read, and a second mode in which an image of the original M is read while the original M is being transported by the original transport unit 21. For example, a first sensor (not shown) that detects the original M placed on the second platen glass 32, and a second sensor (for example, an optical sensor or a sensor with a mechanical lever switch structure; not shown) that detects the original M placed on the original tray 23 of the original transport unit 21 are provided. When the original M is detected by the first sensor, the first mode is set, and when the original M is detected by the second sensor, the second mode is set.

[0017] In the first mode, the document transport unit 21 is opened, and the second platen glass 32 of the reading unit 22 is opened. The document transport unit 21 is then closed, and the document transport unit 21 presses down on the document M placed on the second platen glass 32. In the reading unit 22, the carriage 34 and the optical system unit 35 are moved in the sub-scanning direction X while maintaining a predetermined speed relationship. Light from the light source 34A of the carriage 34 is irradiated onto the document M via the second platen glass 32, and the light reflected by the document M is reflected by the mirror 34B of the carriage 34. This light is then reflected by the mirrors 35A and 35B of the optical system unit 35 and enters the CCD sensor 37 through the condenser lens 36. The CCD sensor 37 repeatedly reads the image of the document M in the main scanning direction Y (a direction perpendicular to the sub-scanning direction X).

[0018] In the second mode, with the document transport unit 21 closed, the document M placed on the document tray 23 is pulled out one by one by the paper feed roller 24 of the document transport unit 21, the document M is transported in the sub-scanning direction over the first platen glass 31 by the registration roller 25 and each transport roller 26, and the document M is discharged onto the document discharge tray 28 by the paper discharge roller 27. In the reading unit 22, the carriage 34 and the optical system unit 35 are positioned at their respective predetermined positions below the first platen glass 31, light from the light source 34A of the carriage 34 is irradiated onto the document M through the first platen glass 31, the light reflected by the document M is reflected by each mirror 34B, 35A, 35B, and made to enter the CCD sensor 37 through the condenser lens 36, and the image of the document M is repeatedly read by the CCD sensor 37 in the main scanning direction Y.

[0019] 3 is a block diagram showing the internal configuration of the image reading device 10. The image reading device 10 includes a document transport unit 21, a reading unit 22, an operation unit 41, a temperature sensor 42, a storage unit 43, and a control unit 44. These components are capable of transmitting and receiving data or signals to and from each other via a bus.

[0020] The document transport unit 21 is a so-called automatic document feeder, and includes a motor 46 that rotates and drives each transport roller 26. The motor 46 is, for example, a stepping motor.

[0021] The operation unit 41 includes physical keys such as a numeric keypad, a decision key, and a start key.

[0022] The temperature sensor 42 includes a non-contact infrared sensor or the like, and detects the ambient temperature of the motor 46 of the document transport unit 21. Note that the temperature sensor 42 may be a thermometer that can detect the ambient temperature of the motor 46 of the document transport unit 21, and is not limited to a non-contact infrared sensor.

[0023] The storage unit 43 is a large-capacity storage device such as an SSD (Solid State Drive) or an HDD (Hard Disk Drive), and stores various application programs and various data.

[0024] The control unit 44 is composed of a processor, a RAM (Random Access Memory), a ROM (Read Only Memory), etc. The processor is, for example, a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), or an MPU (Micro Processing Unit). The control unit 44 functions as a control unit 45 when a control program stored in the ROM or the storage unit 43 is executed by the processor.

[0025] The control unit 44 comprehensively controls the image reading device 10. The control unit 44 is connected to the document transport unit 21, the reading unit 22, the operation unit 41, the temperature sensor 42, the storage unit 43, etc., and controls the operation of these components and transmits and receives signals or data to and from each of the components.

[0026] The motor 46 of the document transport unit 21 corresponds to the motor in the claims, the temperature sensor 42 corresponds to the temperature sensor in the claims, and the control unit 45 corresponds to the control unit in the claims.

[0027] In image reading device 10, for example, when a user places multiple documents M on document tray 23 of document transport unit 21 and operates the start key on operation unit 41, and a document reading instruction is received by operation unit 41, control unit 45 sets the second mode in accordance with the document reading instruction. When documents M are detected by the second sensor, control unit 45 causes paper feed roller 24 to pull out documents M placed on document tray 23 one by one, causes registration roller 25 and each transport roller 26 to transport documents M in the sub-scanning direction over first platen glass 31, and causes discharge roller 27 to discharge documents M onto document discharge tray 28, and at this time causes reading unit 22 to read the image of documents M through first platen glass 31.

[0028] At this time, since the document transport unit 21 continuously transports multiple documents M, the motor 46 of the document transport unit 21, which rotates and drives each transport roller 26, continues to be driven and becomes overloaded, causing the temperature of the motor 46 to rise and the motor 46 to tend to overheat, so it is necessary to deal with the temperature rise of the motor 46.

[0029] In this embodiment, the control unit 45 determines the maximum temperature T max The control unit 45 calculates the rising temperature Tj of the motor 46, which rises with the time t that the motor 46 is operating, and also calculates the falling temperature Tj of the motor 46, which falls with the time t that the motor 46 is stopped. Then, when the rising temperature Tj of the motor 46 exceeds a preset first temperature threshold TS1 of the motor 46 while the motor 46 is operating, the control unit 45 stops the motor 46. This is to cool the motor 46 by heat dissipation. Furthermore, when the falling temperature Tk of the motor 46 falls below a lower preset second temperature threshold TS2, the control unit 45 resumes operation of the motor 46. This is to prevent the motor 46 from overheating.

[0030] More specifically, if the temperature of the motor 46 is T, the known electrical resistance of the windings of the motor 46 when the temperature T of the motor 46 reaches a predetermined reference temperature T0 is R0, and the temperature coefficient of the resistance of the windings of the motor 46 is α, the electrical resistance R(T) of the windings of the motor 46 when the temperature of the motor 46 is T is expressed by the following equation (D). R(T)=R0*(1+α*(T-T0)) …Formula (D)

[0031] The ambient temperature of the motor 46 detected by the temperature sensor 42 is T amb The power supplied to the motor 46 is P, and the thermal resistance between the windings of the motor 46 and the ambient space is R. th Then, the temperature T of the motor 46 is expressed by the following equation (E). T=R th *P+T amb …Formula (E)

[0032] If the current supplied to the motor 46 is I, then P=R(T)*I 2 =R0*(1+α*(T-T0))*I 2 The following formula (A) is derived based on the above formula (D) and formula (E). T=R th *R0*(1+α*(T-T0))*I 2 +T amb …Formula (A)

[0033] From this, the control unit 45 calculates the temperature T of the motor 46 based on the above formula (A), and calculates the calculated temperature T as the maximum temperature T of the motor 46. max Set as.

[0034] Thus, the maximum temperature T of the motor 46 max is the electrical resistance R0 of the windings of the motor 46, the temperature T of the motor 46, the reference temperature T0 of the motor 46, the temperature coefficient α of the resistance of the windings of the motor 46, and the thermal resistance R between the windings of the motor 46 and the ambient space. th , the current I supplied to the motor 46, and the ambient temperature T of the motor 46. amb It is determined by the thermal resistance R thcorresponds to the heat dissipation of the motor 46, and R0(1+α*(T-T0))*I 2 is the power P and corresponds to the heat generation amount of the motor 46, so the heat dissipation of the motor 46, the heat generation amount of the motor 46 (power P), and the ambient temperature T amb The maximum temperature of the motor 46 T max is decided.

[0035] Then, assuming that the thermal time constant of the motor 46 is τ and e is the Napier's number, the control unit 45 calculates the rising temperature Tj of the motor 46, which rises with the time t that the motor 46 is operating, based on the following equation (B) while the motor 46 is operating. Tj=T amb +(T max -T amb )*(1-e -t / τ) …(B)

[0036] Furthermore, when the motor 46 is stopped, the control unit 45 calculates the falling temperature Tk of the motor 46, which falls with the time t that the motor 46 is stopped, based on the following formula (C). Tk=T amb +(T max -T amb )*e -t / τ …(C)

[0037] The control unit 45 operates the motor 46, and the rising temperature Tj of the motor 46 reaches the maximum temperature T max When the falling temperature Tk of the motor 46 exceeds a preset first temperature threshold TS1 that is lower than the first temperature threshold TS1, the control unit 45 stops the motor 46. This allows the motor 46 to cool down by heat radiation. Furthermore, when the falling temperature Tk of the motor 46 falls below a preset second temperature threshold TS2 that is lower than the first temperature threshold TS1, the control unit 45 restarts the operation of the motor 46. This causes the temperature T of the motor 46 to be lower than the maximum temperature T max This keeps the temperature lower than the normal range to prevent the motor 46 from overheating.

[0038] The known electrical resistance R of the windings of the motor 46 when the temperature T of the motor 46 reaches the reference temperature T is the temperature coefficient α of the resistance of the windings of the motor 46, and the thermal resistance R between the windings of the motor 46 and the ambient space. th The thermal time constant τ of the motor 46, the Napier's number e, and the current I (for example, rated current) supplied to the motor 46 are set in advance and stored in the memory unit 43. The control unit 45 reads and acquires these values ​​from the memory unit 43, and also acquires the ambient temperature T of the motor 46 detected by the temperature sensor 42. amb is obtained and the above formulas (A) to (E) are calculated.

[0039] 4 is a graph showing the characteristics of the temperature rise Tj of the motor 46, which is expressed by the above formula (B). As is clear from the graph of FIG. 4, the temperature rise Tj of the motor 46 varies depending on the ambient temperature T amb It rises with the passage of time t from max The first temperature threshold TS1 is set to the maximum temperature T max For example, the maximum temperature T max If the temperature is expected to be 100°C or higher, the first temperature threshold TS1 is set to 90°C.

[0040] 5 is a graph showing the characteristics of the falling temperature Tk of the motor 46, which is expressed by the above formula (C). As is clear from the graph of FIG. 5, the falling temperature Tk of the motor 46 is proportional to the maximum temperature T max The temperature of the motor 46 decreases as time t passes. amb The second temperature threshold TS2 is set to be lower than the first temperature threshold TS1. For example, if the first temperature threshold TS1 is set to 90°C, the second temperature threshold TS2 is set to 80°C.

[0041] 6 is a graph showing the temperature change of the motor 46 controlled by the control unit 45. As is clear from the graph of FIG. 6, the temperature rise Tj of the motor 46 increases as the ambient temperature T ambThe temperature rises as time t passes from TS1, and when it exceeds the first temperature threshold value TS1, it drops due to the motor 46 stopping and heat dissipation. When it falls below the second temperature threshold value TS2, it rises due to the motor 46 restarting operation. The temperature fluctuates around the first temperature threshold value TS1 and the second temperature threshold value TS2, and reaches the maximum temperature T max It will never reach

[0042] Furthermore, in the image reading device 10, the load on the motor 46, which is the power source for transporting the document in the document transport unit 21, varies depending on the reading resolution of the document by the reading unit 22. For example, the transport speed of the document M is changed depending on the reading resolution of the document M by the reading unit 22, and the load on the motor 46 varies.

[0043] In this case, the temperature rise Tj calculated by the above formula (B) must be changed for each document reading resolution. For example, suppose that the temperatures T11, T21, T31, and T41 are calculated for each document reading resolution, and formulas F1(t11), G1(t21), H1(t31), and Y1(t41) are set to calculate the temperatures T11, T21, T31, and T41. The formulas F1(t11), G1(t21), H1(t31), and Y1(t41) are used to correct the values ​​included in the above formula (B) and calculate the temperature rise of the motor 46 according to the document reading resolution.

[0044] T11=F1(t11), T21=G1(t21), T31=H1(t31), T41=Y1(t41)

[0045] Furthermore, the falling temperature Tk calculated by the above formula (C) must be corrected for each reading resolution of the original M. For example, suppose that the falling temperatures T12, T22, T32, and T42 are calculated for each reading resolution of the original M, and formulas F2(t12), G2(t22), H2(t32), and Y2(t42) are set to calculate the falling temperatures T12, T22, T32, and T42. The formulas F2(t12), G2(t22), H2(t32), and Y1(t42) are used to correct the values ​​included in the above formula (C) and calculate the falling temperature of the motor 46 according to the reading resolution of the original. T12=F2(t12), T22=G2(t22), T32=H2(t32), T42=Y2(t42)

[0046] As a result, even if the reading resolution of the original M is changed, the rising and falling temperatures of the motor 46 can be calculated with high precision, and the motor 46 can be prevented from overheating.

[0047] Next, the control procedure of the motor 46 by the control unit 45 will be described with reference to the flowchart shown in FIG.

[0048] The control unit 45 detects the ambient temperature T of the motor 46 detected by the temperature sensor 42 at regular intervals (for example, every 1 msec). amb The control unit 45 also obtains the known electrical resistance R0 of the windings of the motor 46 when the temperature T of the motor 46 reaches the reference temperature T0, the temperature coefficient α of the resistance of the windings of the motor 46, and the thermal resistance R between the windings of the motor 46 and the ambient space. th The thermal time constant τ of the motor 46, the Napier's number e, and the current I supplied to the motor 46 are read and acquired from the storage unit 43 (S101).

[0049] The control unit 45 detects the ambient temperature T amb , the known electrical resistance R0 of the windings of the motor 46, the temperature coefficient of resistance α of the windings of the motor 46, and the thermal resistance R between the windings of the motor 46 and the ambient space. th , and the current I supplied to the motor 46, the above formulas (D), (E), and (A) are used to calculate the maximum temperature T of the motor 46. max is calculated (S102).

[0050] The control unit 45 determines whether the operation of the motor 46 has started (S103), and if it determines that the operation of the motor 46 has started (S103 "Yes"), it measures the time t that has elapsed since the operation of the motor 46 started, and determines whether the reading resolution of the original M by the reading unit 22 is 300 x 600 dpi, 600 x 300 dpi, 300 x 300 dpi, or 600 x 600 dpi (S104 to S107).

[0051] If the control unit 45 determines that the reading resolution of the original M is 300 × 600 dpi (S104 "Yes"), it selects and sets the above formula F1(t11) and calculates the rising temperature T11 of the motor 46 that rises with the passage of time t from the start of operation of the motor 46 based on the formula F1(t11) (S108). Also, if the control unit 45 determines that the reading resolution of the original M is 600 × 300 dpi (S104 "No", S105 "Yes"), it selects and sets the above formula G1(t21) and calculates the rising temperature T21 of the motor 46 that rises with the passage of time t from the start of operation based on the formula G1(t21) (S109). Furthermore, when the control unit 45 determines that the reading resolution of the original M is 300 × 300 dpi (S104 “No”, S105 “No”, S106 “Yes”), it selects and sets the above formula H1(t31) and calculates the rising temperature T31 of the motor 46 that rises with the passage of time t from the start of operation based on formula H1(t31) (S110). When the control unit 45 determines that the reading resolution of the original M is 600 × 600 dpi (S104 “No”, S105 “No”, S106 “No”, S107 “Yes”), it selects and sets the above formula Y1(t41) and calculates the rising temperature T41 of the motor 46 that rises with the passage of time t from the start of operation based on formula Y1(t41) (S111).

[0052] If the reading resolution of the original M is unknown (S104 "No", S105 "No", S106 "No", S107 "No"), the control procedure in FIG. 7 is temporarily terminated, and the process from S101 is repeated.

[0053] When the control unit 45 calculates the rising temperature of the motor 46 in any of S108 to S111, it determines whether the rising temperature exceeds a first temperature threshold value TS1 (=90°C) (S112), and if the rising temperature is less than the first temperature threshold value TS1 (S112 "No"), it temporarily ends the control procedure in Fig. 7 and repeats the processing from S101 because the motor 46 is not overheated.

[0054] Furthermore, if the rising temperature exceeds the first temperature threshold value TS1 (S112 "Yes"), the control unit 45 stops the motor 46 and sets the cooling mode to cool the motor 46 by dissipating heat (S113), because the motor 46 is overheated.

[0055] When the cooling mode is set, the control unit 45 measures the time t that has elapsed since the motor 46 stopped, and determines whether the reading resolution of the original M by the reading unit 22 is 300×600 dpi, 600×300 dpi, 300×300 dpi, or 600×600 dpi (S114 to S117).

[0056] If the control unit 45 determines that the reading resolution of the original M is 300 x 600 dpi (S114 "Yes"), it selects and sets the above formula F2(t12) and calculates the falling temperature T22 of the motor 46 that decreases as the time t elapses since the motor 46 has stopped based on the formula F2(t12) (S118). If the control unit 45 determines that the reading resolution of the original M is 600 x 300 dpi (S114 "No", S115 "Yes"), it selects and sets the above formula G2(t22) and calculates the falling temperature T22 of the motor 46 that decreases as the time t elapses since the motor 46 has stopped based on the formula G2(t22) (S119). Furthermore, when the control unit 45 determines that the reading resolution of the original M is 300 × 300 dpi (S114 “No”, S115 “No”, S116 “Yes”), it selects and sets the above formula H2(t32) and calculates the falling temperature T32 of the motor 46 that decreases with the passage of time t since the motor 46 has stopped based on the formula H2(t32) (S120). Furthermore, when the control unit 45 determines that the reading resolution of the original M is 600 × 600 dpi (S114 “No”, S115 “No”, S116 “No”, S117 “Yes”), it selects and sets the above formula Y2(t42) and calculates the falling temperature T42 of the motor 46 that decreases with the passage of time t since the motor 46 has stopped based on the formula Y2(t42) (S121).

[0057] If the reading resolution of the original M is unknown (S114 "No", S115 "No", S116 "No", S117 "No"), the control procedure in FIG. 7 is temporarily terminated, and the process from S101 is repeated.

[0058] When the control unit 45 calculates the falling temperature of the motor 46 in any of S118 to S121, it checks whether the cooling mode is set (S122), and if the cooling mode is set (S122 "Yes"), it determines whether the falling temperature is less than the second temperature threshold value TS2 (S123), and if the falling temperature is less than the second temperature threshold value TS2 (S123 "Yes"), it resumes the operation of the motor 46 and cancels the cooling mode (S124). In this case, this is because the motor 46 has been cooled.

[0059] Furthermore, if the falling temperature is not less than the second temperature threshold value TS2 (S123 "No"), the control unit 45 does not cancel the cooling mode, temporarily ends the control procedure in FIG. 7, and repeats the process from S101.

[0060] 7 and repeats the process from S101. For example, when the image reading device 10 is not reading an image of the original M, the motor 46 does not operate (S103 "No"), the cooling mode is not set in S113, and the process proceeds to S122 via S114 to S117 and S118 to S121. In this case, it is determined that the cooling mode is not set (S122 "No"), and the process returns to S101.

[0061] As described above, in this embodiment, the control unit 45 calculates the maximum temperature, rising temperature, and falling temperature of the motor based on basic characteristics such as the electrical resistance and temperature coefficient of the motor windings, operates the motor 46, stops the motor 46 when the rising temperature of the motor 46 exceeds the first temperature threshold TS1, and cools the motor 46 by heat dissipation, and resumes operation of the motor 46 when the falling temperature of the motor 46 falls below the second temperature threshold TS2, thereby preventing overheating of the motor 46. In other words, according to this embodiment, the temperature of the motor 46 is calculated based on basic characteristics such as the electrical resistance and temperature coefficient of the motor 46 windings, and control can be performed to prevent the motor from overheating without using a cooling fan or a motor temperature sensor.

[0062] In the above embodiment, the motor 46 that rotates and drives the transport rollers 26 for feeding the document is exemplified, but the present invention can also be applied to other motors.

[0063] Furthermore, the configurations and processes of the above-described embodiment explained using FIGS. 1 to 7 are merely examples of the present invention, and the present invention is not limited to these configurations and processes. [Explanation of symbols]

[0064] 10 Image reader 21 Document transport section 22 Reading unit 41 Operation section 42 Temperature Sensor 43 Storage section 44 Control Unit 45 Control Unit 46 Motor

Claims

1. A motor and a temperature sensor for detecting an ambient temperature of the motor; a control unit that controls the motor, The temperature of the motor is T, and the preset reference temperature of the motor is T 0 and the reference temperature T 0 The known electrical resistance of the motor winding at this time is R 0 The temperature coefficient of the resistance of the winding of the motor is α, and the ambient temperature of the motor detected by the temperature sensor is T amb , and the thermal resistance between the motor winding and the ambient space is R th , where I is the current supplied to the motor, The control unit T=R th *R 0 * (1 + α * (T - T 0 )) *I 2 +T amb Using formula (A) consisting of: The temperature T of the motor is calculated based on the formula (A), and the calculated temperature T is the maximum temperature T of the motor. max Set it as When the thermal time constant of the motor is τ and the Napier's number is e, the rising temperature Tj of the motor, which rises with the time t during which the motor is operating, is calculated based on the following equation (B): Tj = T amb + (T max - T amb ) * (1 - e -t / τ) … Equation (B) When the motor is stopped, a falling temperature Tk of the motor, which falls with the time t during which the motor is stopped, is calculated based on the following formula (C): Tk = T amb + (T) max -D amb )*e -t / τ ... formula (C) A motor control device that operates the motor, stops the motor when a rising temperature Tj of the motor exceeds a predetermined first temperature threshold TS1, and resumes operation of the motor when a falling temperature Tk of the motor becomes less than a predetermined second temperature threshold TS2 that is lower than the first temperature threshold TS1.

2. The formula (A) is The formula (D) shows the electrical resistance R(T) of the motor winding when the temperature T of the motor is: R(T) = R 0 * (1 + α * (T - T 0 ))and, When the power supplied to the motor is P, the temperature T of the motor is expressed by the formula (E): T = R th *P+T amb 2. The motor control device of claim 1, wherein the motor control device is derived by:

3. The motor control device according to claim 1 or 2; a document transport unit that transports a document using a motor of the motor control device; a reading unit that reads an image of the document; The control unit of the motor control device corrects the numerical values ​​contained in the formulas B and C according to the reading resolution of the image of the document by the reading unit, and calculates the rising temperature and falling temperature of the motor according to the reading resolution.

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