Fan Controller and Image Forming Apparatus

Abstract

A fan controller and an image forming apparatus are provided. The fan controller includes a rotational frequency instructing unit configured to output driving instructions to a fan driving unit that is configured to control a rotational frequency of a fan, the driving instructions including a target value of the rotational frequency of the fan; a rotational frequency detection unit configured to detect an actual measurement value of the rotational frequency of the fan; a storage unit configured to store consecutively at given time intervals a plurality of parameters indicating a correspondence relationship between the driving instructions output by the rotation frequency instructing unit and the rotational frequency detected by the rotational frequency detection unit; and a notification unit configured to notify a condition of the fan on the basis of the plurality of parameters. The image forming apparatus includes a fan, a fan driver and the fan controller.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No. 2008-050263 filed on Feb. 29, 2008, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

Apparatuses and devices consistent with the present invention relate to controlling a fan and, more particularly, to controlling a fan used in an image forming apparatus whereby a condition of the fan is monitored.

BACKGROUND

In the related art, a fan is often provided to cool various types of apparatuses including an image forming apparatus. Japanese Published Unexamined Patent Application No. 2006-280162 describes maintaining a rotational frequency of a related art fan by reducing a number of resistance elements when the consumption of current of the fan increases over a length of time.

However, the related art fan has a disadvantage in that, if the consumption of current of the fan is great at a certain point in time, it is impossible to carry out control of the rotational frequency of the fan at a later time on the basis of past conditions.

SUMMARY

Exemplary embodiments of the present invention address the above disadvantages and other disadvantages not described above. However, the present invention is not required to overcome the disadvantages described above, and thus, an exemplary embodiment of the present invention may not overcome any of the disadvantages described above.

Accordingly, illustrative aspects of the present invention provide a fan controller capable of notifying a condition of the fan on the basis of conditions of the fan and an image forming apparatus in which the fan controller is used.

According to an aspect of the present invention, there is provided a fan controller comprising a rotational frequency instructing unit configured to output driving instructions to a fan driving unit that is configured to control a rotational frequency of a fan, the driving instructions comprising a target value of the rotational frequency of the fan; a rotational frequency detection unit configured to detect an actual measurement value of the rotational frequency of the fan; a storage unit configured to store consecutively at given time intervals a plurality of parameters indicating a correspondence relationship between the driving instructions output by the rotation frequency instructing unit and the rotational frequency detected by the rotational frequency detection unit; and a notification unit configured to notify a condition of the fan on the basis of the plurality of parameters.

According to another aspect of the present invention, there is provided an image forming apparatus comprising a fan; a fan driver; and a fan controller. The fan driver is configured to control a rotation frequency of the fan. The fan controller comprises a rotational frequency instructing unit which outputs driving instructions to the fan driver, the driving instructions comprising a target value of the rotational frequency of the fan; a frequency detector which detects an actual measurement value of the rotational frequency of the fan; a memory which consecutively at given time intervals stores a plurality of parameters indicating a correspondence relationship between the driving instructions output by the rotational frequency instructing unit and the rotational frequency detected by the frequency detector; and a notification unit which indicates a condition of the fan on the basis of the plurality of parameters.

According to yet another aspect of the present invention, there is provided a fan controller comprising an integrated circuit comprising a rotational frequency instructing circuit which outputs driving instructions to a fan driver that is configured to control a rotational frequency of a fan, the driving instructions comprising a target value of the rotational frequency of the fan; a frequency detector which detects an actual measurement value of the rotational frequency of the fan; a memory circuit which consecutively at given time intervals stores a plurality of parameters indicating a relationship between the driving instructions output by the rotational frequency instructing circuit and the rotational frequency detected by the frequency detector; and a notification circuit which indicates a condition of the fan on the basis of the plurality of parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the appearance of an image forming apparatus according to an exemplary embodiment of the present invention;

FIG. 2 is a circuit diagram showing an example of a constitution of a driving system according to an exemplary embodiment of the present invention;

FIG. 3 is a circuit diagram showing an example of a constitution of a driving system according to another exemplary embodiment of the present invention;

FIG. 4 is a view for explaining a relationship between driving instructions and a rotational frequency in each of the driving systems;

FIG. 5 is a flow chart showing control processing for the fan according to an exemplary embodiment of the present invention; and

FIG. 6 is a view for explaining relationships of various values in the control processing.

DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

Next, a description will be given for an exemplary embodiment of the present invention by referring to the drawings. In this exemplary embodiment, the present inventive concept is applied to an image forming apparatus.

1. Image Forming Apparatus

FIG. 1 is a perspective view showing the appearance of an image forming apparatus 1 of the present exemplary embodiment. The image forming apparatus is embodied as a laser printer 1. The laser printer 1 is installed, with the upper side on the page space given as the upper side in the gravitational direction, and usually used, with the left near side on the page space given as the front side.

The laser printer 1 includes a housing 3 formed approximately in a box shape (rectangular solid shape). A paper discharging tray 5 on which a printed medium that has been printed and discharged from the housing 3 is provided on the upper face of the housing 3. In the present exemplary embodiment, paper and sheets such as overhead projector (OHP) sheets are used as printed media. Alternatively, other types of paper and sheets may be used.

The paper discharging tray 5 is constituted to give an inclined face 5a which is inclined in such a manner as to lower from the upper face of the housing 3 to the rear side. A discharge portion 7 at which the printed medium completed for printing is discharged is provided at the rear end of the inclined face 5a.

An upper cover 9 formed in approximately a U-letter shape so as to enclose the paper discharging tray 5 (inclined face 5a) of the housing 3 is provided with a line switch 1a for switching the connection of the laser printer 1 to, e.g., a network. The laser printer 1 is also provided with a job cancellation switch 1b for forcibly terminating (discontinuing) printing, a display panel 1c as one example of a notification unit configured to display various types of information, and others. Alternatively, the notification unit may be a unit configured to generate a notification signal or an output pin on the ASIC 50 which is connected to an external notification device, such as a display, light emitting diode (LED), or audible alarm.

The laser printer 1 is provided at the lower part of the housing 3 with a paper feeding cassette 11 which may be attached to or detached therefrom. There is provided inside the housing 3 a printer engine (not illustrated) which forms (prints) an image on a printed medium accommodated in the paper feeding cassette 11 by an electro-photographic process and discharges the printed medium from a discharge portion 7. Further, on the side face of the housing 3, there are provided fans 41, 42 for cooling the printer engine or the power section, etc., accommodated inside the housing 3. Two fans 41, 42 are shown in FIG. 1. However, alternatively, one fan or a plurality of fans may be provided.

2. Driving System of the Fan

Next, a description will be given of an example of a constitution of a driving system of the fans 41, 42. The driving system is an example of the fan controller. In addition, since the driving system of the fans 41, 42 are substantially similar in constitution, only the driving system of the fan 41 will be hereinafter described.

FIG. 2 is a circuit diagram showing an example of a constitution of the driving system of the fan 41. As shown in FIG. 2, the fan 41 (FAN) is controlled by an application specific integrated circuit (ASIC) 50 equipped with a central processing unit (CPU) 51, a read only memory (ROM) 52 and a random access memory (RAM) 53. The CPU is an example of a rotational frequency instructing unit. A Frequency Generator (FG) signal is input from the fan 41 to an FGIN terminal. The FGIN terminal is an example of a rotational frequency detection unit of the ASIC 50. In addition, the display panel 1c is also connected to the ASIC 50. Further, the ASIC 50 is provided with a FAN_H terminal for driving the fan 41 at a high speed, a FAN_M terminal for driving the fan 41 at a medium speed, and a FAN_L terminal for driving the fan 41 at a low speed. The FAN_H terminal, the FAN_M terminal and the FAN_L terminal suppply a driving voltage to an input terminal FAN_IN of the fan 41 via a driving circuit 60. Specifically, the FAN_H terminal, the FAN_L terminal, the FAN_M terminal and the driving circuit 60 correspond to a fan driving unit.

A detailed description will now be given of an example of a constitution of the driving circuit 60. As shown in FIG. 2, the FAN_H terminal is connected via a resistor R2 to a base of a transistor Tr1 in which the base is connected to an emitter via a resistor R1. The emitter of the transistor Tr1 is grounded, and a collector is connected via a resistor R4 to a base of a transistor Tr2 in which the base is connected to an emitter via a resistor R3. The emitter of the transistor Tr2 is connected to a direct current power source. A 24V direct current power source is shown in FIG. 2. However, the specific value of the direct current power source may be different. The collector of the transistor Tr2 is connected to the input terminal FAN_IN of the fan 41. Therefore, when an “H” level signal is output from the FAN_H terminal, an direct voltage, which is approximately equal to the voltage of the direct current power source (in this case, 24V) is supplied to the input terminal FAN_IN, thus making it possible to drive the fan 41 at a high speed.

The FAN_M terminal is connected via a resistor R7 to a base of a transistor Tr3 in which the base is connected via a resistor R6 to an emitter. The emitter of the transistor Tr3 is grounded, and a collector is connected via a resistor R9 to a base of a transistor Tr4 in which the base is connected via a resistor R8 to an emitter. The emitter of the transistor Tr4 is connected via a Zener diode D1 to the direct current power source, and the collector is connected to the input terminal FAN_IN of the fan 41. Thus, when an “H” level signal is output from the FAN_M terminal, a direct voltage obtained by subtracting a voltage drop due to the Zener diode D1 from the voltage of the direct current power source (in this case 24V) is supplied to the input terminal FAN_IN, thus making it possible to drive the fan 41 at a medium speed.

The FAN_L terminal is connected via a resistor R12 to a base of a transistor Tr5 in which the base is connected via a resistor R11 to an emitter. The emitter of the transistor Tr5 is grounded, and a collector is connected via a resistor R14 to a base of a transistor Tr6 in which the base is connected via a resistor R13 to an emitter. The emitter of a transistor Tr12 is connected via Zener diodes D2, D3 to the direct current power source, and the collector is connected to the input terminal FAN_IN of the fan 41. Thus, when an “H” level signal is output from the FAN_L terminal, a direct current voltage obtained by subtracting a voltage drop due to the Zener diodes D2, D3 from the voltage of the direct current power source (in this case 24V) is supplied to the input terminal FAN_IN, thus making it possible to drive the fan 41 at a low speed. Another driving terminal, such as, e.g., a super low driving terminal and circuit (three Zener diodes are connected in series) may be also provided.

FIG. 3 shows an example of a constitution of the driving circuit according to another exemplary embodiment of the present invention. In FIG. 2, an instance where an analog direct current voltage is supplied to the input terminal FAN_IN of the fan 41 was illustrated. However, alternatively, a pulse width modulated (PWM) signal may be input to the input terminal FAN_IN of the fan 41 to drive the fan. In such a case, the driving system of the fan 41 may be constituted as shown in FIG. 3. Specifically, in this case, a control (CTL) signal as the PWM signal is directly input from a FAN_CTL signal terminal of the ASIC 50 to the input terminal FAN_IN of the fan 41, thus making it possible to drive the fan 41 at a speed corresponding to the duty ratio of the CTL signal.

3. Control Processing of the Fan

In either instance, as shown in FIG. 4, the greater the voltage input to the fan 41 or the greater the duty ratio (PWM DUTY) of the CTL signal input to the FAN 41, the more the rotational frequency of the fan 41 increases. The rotational frequency of the fan 41 will increase substantially in proportion to the voltage or the duty ratio until the rotational frequency reaches a certain value, and will not increase any more when the rotational frequency reaches the certain value.

A value R obtained by dividing the rotational frequency by the voltage or the duty ratio is adopted as a parameter indicating a correspondence relationship between the driving instructions (the voltage or duty ratio) input to the fan 41 and a rotational frequency of the fan 41, thereby executing the control shown below.

FIG. 5 is a flow chart of control processing according to an exemplary embodiment of the present invention. The control processing is provided to the fan 41. The control processing is started at a time when the laser printer 1 is switched on and the fan 42 is also controlled similarly and concurrently. Further, the above-described parameter R is stored in a log in chronological order in the RAM 53 during the execution of the control processing. Specifically, the logs of parameters R are stored in the RAM 53 at given time intervals while the image forming apparatus is powered on. If a new parameter R is to be stored after a given number of the parameters R are stored in the RAM 53, an oldest one of the parameters R in the RAM 53 is erased and then the new parameter R is stored in the RAM 53. The RAM 53 is one example of a storage unit.

As shown in FIG. 5, in the control processing, in S1, the fan 41 is first rotated and driven. In S2, counters Nh and N1 to be described later are reset to 0. In S3, it is determined whether R is greater than a value Rmax. If it is determined that R is greater than the threshold value Rmax (S3: Y), an error message, such as “Fan error” and/or “Call a technician” is displayed on the display panel 1c. Then, the processing proceeds to S5. In S5, the laser printer 1 as a whole including the fan 41 is halted and the processing is temporarily completed. On the other hand, if it determined that R≦Rmax, (S3: N), the processing proceeds to S6, and it is determined whether R is less than a minimum value Rmin. If it is determined that R<Rmin (S6: Y), the processing proceeds to the above-described S4, and if it is determined that R≧Rmin (S6: N), the processing proceeds to S10.

In S10, it is determined whether R is greater than an upper limit Rh. Rh denotes a value at which the value R is deviated towards a higher rotational frequency within a permissible range. If it is determined that R≦Rh (S10:N), a counter Nh is reset to be 0 in S11, and the processing proceeds to S20 to be described later. On the other hand, if it is determined that R>Rh (S10:Y), the counter Nh is incremented by one in S12, and it is determined whether the counter Nh is in excess of 100 in S13. If it is determined that Nh≦100 (S13:N), the processing proceeds to S20. If it is determined that the counter Nh>100 (S13:Y), an error message such as, e.g., “Fan error” and/or “Call a technician” is displayed on the display panel 1c, and the processing proceeds to the previously described S5. In other words, the counter Nh is a counter for counting the number of times at which R is consecutively in excess of an upper limit Rh of the target value within a threshold range (e.g., Rmin≦R≦Rmax). In this case, the number of times is set at 100. However, the number of times may be set to a different threshold number.

In S20, it is determined whether R is less than a lower limit R1. R1 denotes a value at which the value R is deviated towards a lower rotational frequency within a permissible range. If it is determined that R≧R1 (S20:N), the counter N1 is reset to be 0 in S21, and the processing proceeds to S30 to be described later. On the other hand, if it is determined that R<R1 (S20:Y), the counter N1 is incremented by one in S22, and it is determined whether the counter N1 is in excess of 100. If it is determined that the counter N1>100 (S23:Y), an error message such as “Fan error” and/or “Clean the fan” is displayed on the display panel 1c, and the processing proceeds to the previously described S5. In other words, the counter N1 is a counter for counting a number of times at which R is consecutively in excess of a lower limit R1 of the target value within a threshold range (Rmin≦R≦Rmax). In this case, the number of times is set at 100. However, the number of times may be set to a different threshold number.

If it is determined that the counter N1≦100 (S23:N), it is determined whether a difference d obtained by subtracting the previously obtained R from the presently obtained R is lower than a threshold value of the difference (negative value) D. If it is determined that the difference d is lower than the threshold value D (S25:Y), an error message such as “Fan error” and/or “Call a technician” is displayed on the display panel 1c, and the processing proceeds to the previously described S5. On the other hand, if it is determined that D≦d (S25:N), it is determined whether a value obtained by doubling the presently obtained R is lower than an average value (Rave) of R so far obtained. If it is determined that 2R<Rave (S27:Y), an error message such as “Fan error” and/or “Call a technician” is displayed on the display panel 1c, and the processing proceeds to the previously described S5.

On the other hand, if it is determined that 2R≧Rave (S27:N), the processing proceeds to S30. In S30, after a standby period, the processing proceeds to the previously described S3. The standby period may be approximately one hour, or another period.

Due to the control processing according to an exemplary embodiment of the present invention, it is possible to notify in detail as described below a condition of the fan 41 on the basis of a plurality of the parameters R stored in chronological order. That is, as shown in FIG. 6, R is set so as to be between target values Rh, R1 and within a threshold range specified by Rmax, Rmin. Specifically, there are set a median value R0 and an upper limit Rh and a lower limit R1 of a range in which the target value R can be regarded as the median value R0. The threshold range is, for example, a permissible range which is be determined as a range in which the fan normally operates. In addition, in FIG. 6, the longitudinal axis is given as “rotational frequency/voltage,” which corresponds to the driving system shown in FIG. 2. Thus, where the driving system shown in FIG. 3 is adopted, the longitudinal axis is given as “rotational frequency/duty ratio.”

Then, a case in which R is outside of the target values and the threshold range (S3:Y or S6:Y, i.e., R>Rmax or R<Rmin), the ASIC 50 determines as an error to display the error, thereby halting the apparatus (S4, S5). Further, a case in which R is within the threshold range but remains higher than the upper target value (i.e., Rmin≦R≦Rmax, and R>Rh) for a certain period of time or longer (S13:Y), the ASIC 50 determines that a driving circuit 61 for driving the fan 41 or the like fails, thus displaying an error, and halting the apparatus (S14,S5).

Further, a case in which R is within the threshold range but remains lower than the lower target value (i.e., Rmin≦R≦Rmax, and R≦R1) for a certain period of time or longer (S23:Y), the ASIC 50 determines that the contamination by foreign matter such as dust prevents the rotation of the fan 41, thus displaying an error requesting cleaning of the fan 41 to halt the apparatus (S24,S5).

Still further, a case in which R decreases extremely (S25:Y or S27:Y), the ASIC 50 determines that an abnormality has occurred in which something other than dust prevents the rotation of the fan 41, thus displaying an error to halt the apparatus (S26, S28, S5). Accordingly, it is possible to notify in detail a condition of the fan 41.

In addition, the present inventive concept shall not be limited to the above-described exemplary embodiments in any way, but may be executed in various exemplary embodiments within the scope of the appended claims. For example, in the above exemplary embodiments, where foreign matter such as dust prevents the rotation of the fan 41 (S23:Y), error messages such as “Fan error” and “Clean the fan” are displayed to halt the apparatus (S4,S5). However, such control may be executed that the fan 41 is automatically rotated at a high speed for a time to remove the dust or the like. In such a case, where the fan 41 is rotated at a high speed during a period of time, the time at which the fan 41 is rotated at high speed may be staggered. For example, the fan may be rotated at high speed when there are few people, for example, at midnight, or when another laser printer 1 is connected to the same network, or when communications are made between the laser printer 1 and another laser printer 1. Thus, it is possible to reduce as much as possible noise generated in association with the rotation of the fan 41 at a high speed.

Further, in the above-described exemplary embodiments, at operations S4, S14, S26, and S28, similar error messages are displayed. However, the display of error messages in these operations may be made different. For example, error codes according to individual errors may be also displayed, depending on causes of individual errors. Still further, the present inventive concept can be applicable to apparatuses other than an image forming apparatus or a laser printer. For example, the present inventive concept is applicable to any apparatus which uses a fan. In addition to the above-described parameters, various parameters may be adopted.

Still further, the value (parameter) R is obtained by dividing the rotational frequency by the voltage or the duty ratio. However, the value (parameter) R may be obtained by dividing an actual measurement value of the rotational frequency of the fan 41 by a target value of the rotational frequency of the fan 41 instructed by the fan controller (ASIC 50).

According to exemplary embodiments of the present invention, a fan controller is provided with a fan driving unit configured to input driving instructions to the fan, a rotational frequency detection unit configured to detect a rotational frequency of the fan, a storage unit configured to store in chronological order a plurality of parameters indicating a correspondence relationship between the driving instructions input by the fan driving unit and the rotational frequency detected by the rotational frequency detection unit, and a notification unit configured to notify a condition of the fan on the basis of the plurality of parameters stored by the storage unit.

The fan driving unit may provide driving instructions to a fan, thereby driving the fan. Further, the storage unit may store in chronological order the plurality of parameters indicating a correspondence relationship between the driving instructions input by the fan driving unit and the rotational frequency detected by the rotational frequency detection unit, and the notification unit may notify a condition of the fan on the basis of the plurality of parameters stored by the storage unit. Therefore, the notification unit is able to notify in chronological order in detail a condition of the fan on the basis of the plurality of parameters stored.

Alternatively, the fan controller according to exemplary embodiments of the present invention may be constituted in such a manner that when values of the plurality of parameters stored by the storage unit are deviated above a higher target range within a threshold range consecutively for a given number of times, the notification unit notifies an error corresponding to the condition thereof. In this case, the notification unit determinates a defective circuit or the like, thus making it possible to notify an error corresponding thereto.

Alternatively, the fan controller according to exemplary embodiments of the present invention may be constituted in such a manner that when values of the plurality of parameters stored by the storage unit are deviated below a lower target range within a threshold range consecutively for a given number of times, the notification unit notifies an error corresponding to the condition thereof. In this case, the notification unit determines that contamination by foreign matter such as dust has occurred, thus making it possible to notify an error corresponding thereto.

Alternatively, the fan controller according to exemplary embodiments of the present invention may be constituted in such a manner that when values of the parameters stored by the storage unit change so as to be in excess of a threshold amount with respect to values of the parameters stored in the past, the notification unit notifies an error corresponding to the condition thereof. In this case, the notification unit determines that the fan is prevented from being rotated due to an abnormality other than dust, thus making it possible to notify an error corresponding thereto. In addition, the values of the parameters stored in the past may be previously stored values, a mean value in the past or other values.

Still further, the above-described parameters may include various parameters, for example a value obtained by dividing a rotational frequency detected by the rotational frequency detection unit by a voltage applied to the fan as the driving instructions by the fan driving unit, or a value obtained by dividing the rotational frequency by a duty ratio of a PWM signal input to the fan as the driving instructions by the fan driving unit.

In addition, an image forming apparatus according to exemplary embodiments of the present invention is that in which any one of the above fan controllers is used. The thus constituted image forming apparatus is able to notify in detail as described above a condition of the fan which cools the interior thereof and others.

While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A fan controller comprising:

a rotational frequency instructing unit configured to output driving instructions to a fan driving unit that is configured to control a rotational frequency of a fan, the driving instructions comprising a target value of the rotational frequency of the fan;

a rotational frequency detection unit configured to detect an actual measurement value of the rotational frequency of the fan;

a storage unit configured to store consecutively at given time intervals a plurality of parameters indicating a correspondence relationship between the driving instructions output by the rotation frequency instructing unit and the rotational frequency detected by the rotational frequency detection unit; and

a notification unit configured to notify a condition of the fan on the basis of the plurality of parameters.

2. The fan controller according to claim 1, wherein when each of a given number of consecutively stored parameters of the plurality of parameters indicates that the actual measurement values are greater than the target value, the notification unit notifies an error corresponding to the condition thereof.

3. The fan controller according to claim 2, wherein when each of a given number of consecutively stored parameters of the plurality of parameters indicates that the actual measurement values are less than the target value, the notification unit notifies an error corresponding to the condition thereof.

4. The fan controller according to claim 1, wherein when each of a given number of consecutively stored parameters of the plurality of parameters indicate that the actual measurement values are less than the target value, the notification unit notifies an error corresponding to the condition thereof.

5. The fan controller according to claim 1, wherein when one parameter of the plurality of parameters indicates that the actual measurement value is lower than the target value and also when a value of the one parameter indicates that a difference between the actual measurement value and the target value is greater than a threshold value, the notification unit notifies an error corresponding to the condition thereof.

6. The fan controller according to claim 1, wherein the driving instructions are a voltage applied to the fan driving unit, and

the parameter is a value obtained by dividing the actual measurement value by the voltage.

7. The fan controller according to claim 1, wherein the driving instructions are a pulse width modulated (PWM) signal, and

the parameter is a value obtained by dividing the actual measurement value by a duty ratio of the PWM signal.

8. An image forming apparatus comprising:

a fan;

a fan driver configured to control a rotation frequency of the fan; and

a fan controller comprising: a rotational frequency instructing unit which outputs driving instructions to the fan driver, the driving instructions comprising a target value of the rotational frequency of the fan; a frequency detector which detects an actual measurement value of the rotational frequency of the fan; a memory which consecutively at given time intervals stores a plurality of parameters indicating a correspondence relationship between the driving instructions output by the rotational frequency instructing unit and the rotational frequency detected by the frequency detector; and a notification unit which indicates a condition of the fan on the basis of the plurality of parameters.

9. A fan controller comprising:

an integrated circuit comprising: a rotational frequency instructing circuit which outputs driving instructions to a fan driver that is configured to control a rotational frequency of a fan, the driving instructions comprising a target value of the rotational frequency of the fan; a frequency detector which detects an actual measurement value of the rotational frequency of the fan; a memory circuit which consecutively at given time intervals stores a plurality of parameters indicating a relationship between the driving instructions output by the rotational frequency instructing circuit and the rotational frequency detected by the frequency detector; and a notification circuit which indicates a condition of the fan on the basis of the plurality of parameters.

10. The fan controller according to claim 9, wherein the fan driver comprises an external driving circuit which comprises a high voltage output circuit, a medium voltage output circuit, and a low voltage output circuit,

wherein the rotational frequency instructing circuit is coupled to the external driving circuit and controls the external driving circuit to output a high voltage, a medium voltage, or a low voltage, as the driving instructions, to the fan based on an output from the fan driver circuit.

11. The fan controller according to claim 9, wherein the driving instructions comprise a pulse width modulated signal.

12. The fan controller according to claim 11, further comprising a controller,

wherein when a value of the plurality of parameters exceeds a first threshold range, the controller controls the notification circuit to indicate a first error and halts a rotation of the fan,

when consecutive values of the plurality of parameters are within the first threshold range but exceed an upper limit of the target value for a given number of times, the controller controls the notification circuit to indicate a second error and halts the rotation of the fan, and

when consecutive values of the plurality of parameters are within the first threshold range but decrease below a lower limit of the target value for a given number of times, the controller controls the notification circuit to indicate a third error and halts a rotation of the fan.