JPH08287544A - Control method for magnetic recording and reproducing device provided with dew condensation sensor - Google Patents

Abstract

PURPOSE: To eliminate a limit in the usage of a magnetic recording and reproducing device based on the erroneous judgement of dew condensation and to prevent a magnetic tape and the magnetic recording and reproducing device from being damaged by the dew condensation by exactly detecting the dew condensation of a rotary cylinder. CONSTITUTION: When any abnormality is detected in the rotation of the rotary cylinder around which the magnetic tape is wound in the state of detecting the dew condensation with a condensation sensor 21, a CPU 1 stops a tape running operation and the rotation of the rotary cylinder. When no abnormality is detected in the rotation of the rotary cylinder around which the magnetic tape is wound, the tape running operation is continued. As a method for detecting abnormality in the rotation of the rotary cylinder, abnormality in the FG signal value of a cylinder 32 for rotating and driving the rotary cylinder or abnormality in the load current value of a cylinder motor 32 for rotating and driving the rotary cylinder is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling a magnetic recording / reproducing apparatus having a rotary cylinder, and more particularly to a method of controlling a magnetic recording apparatus for accurately determining the dew condensation state of the rotary cylinder.

[0002]

2. Description of the Related Art A magnetic tape is wound around a rotary cylinder,
When a magnetic recording device for recording and / or reproducing is moved from a cold atmosphere to a warm atmosphere, dew condensation may occur on the rotating cylinder. Condensation occurs because the heat capacity of the rotating cylinder is large, and thus when the outside air temperature rises rapidly, a large difference occurs between the surface temperature of the rotating cylinder and the outside air temperature. Whether or not dew condensation occurs on the rotating cylinder is related to the difference between the surface temperature of the rotating cylinder and the outside air temperature and the humidity. When recording and / or reproducing operations are performed under the condition that the rotary cylinder is condensed, the frictional resistance between the rotary cylinder and the magnetic tape increases, and the magnetic tape sticks or is entangled with the rotary cylinder. In some cases, the magnetic tape was jammed in the tape running system, and the magnetic recording / reproducing device and the magnetic tape were damaged.

Therefore, conventionally, in order to solve the above-mentioned problem, there is known a device which is provided with a dew condensation sensor inside or outside the magnetic recording device to determine the dew condensation state of the rotary cylinder. The conventional device will be briefly described with reference to the flow chart in FIG. 5. A dew condensation sensor measures dew condensation.
(S1) If it is determined that the magnetic tape is in a dew condensation state (S2, S3), if the magnetic tape is wound around the rotary cylinder to protect the magnetic tape, the magnetic tape is separated from the rotary cylinder. , As an unloading state
(S4), only the command for ejecting the cassette from the magnetic recording / reproducing apparatus is accepted (S5).

Once dew condensation occurs on the rotary cylinder, it usually takes about one hour in the same atmosphere until the dew condensation on the rotary cylinder disappears. Therefore, once the dew condensation sensor detects the dew condensation, the magnetic recording / reproducing apparatus does not accept it for one hour after that, except for the instruction to take out the cassette. After the lapse of 1 hour, the presence / absence of dew condensation is again detected by the dew condensation sensor, and if dew condensation is not detected, the normal tape running operation is performed. Similarly, the magnetic recording / reproducing apparatus does not accept any command other than the cassette eject command.

[0005]

As described above, the detection result of the dew sensor greatly restricts the use of the magnetic recording / reproducing apparatus. Therefore, it becomes necessary for the dew condensation sensor to accurately detect the dew condensation state of the rotary cylinder. Conventionally, a resistance element whose resistance value changes depending on humidity has been widely used as a condensation sensor, and when the resistance value of the resistance element exceeds a preset threshold value, it is determined that there is condensation. . However, the resistance element does not always respond immediately to the degree of wetness of the use atmosphere, and due to differences in the attachment position of the dew condensation sensor to the magnetic recording / reproducing device, the setting of the threshold value of the dew condensation sensor, etc. It may be difficult to accurately detect the condensation state of the rotary cylinder. That is, the dew condensation sensor may determine that dew condensation has occurred on the rotary cylinder even though there is no dew condensation, and such an incorrect determination may prevent the magnetic recording / reproducing apparatus from being used for a certain period of time.

Although the threshold value of the resistance element can be set high so that the dew condensation sensor does not output an erroneous dew condensation detection result, if the threshold value is set high, only severe dew condensation can be detected. Since it disappears, slight dew condensation cannot be detected, which may damage the magnetic recording / reproducing apparatus and the magnetic tape.

In order to solve the above problem, Japanese Patent Laid-Open No. 60-555
No. 39 discloses a device in which a heater is attached to a rotating cylinder. In the apparatus, when the dew condensation sensor detects dew condensation, the magnetic tape is placed in an unloading state and the rotary cylinder is heated by a heater.
The rotating cylinder was heated by the heater until there was no dew condensation detection signal from the dew condensation sensor, and when there was no dew condensation detection signal, heating was stopped and the magnetic tape could be loaded.

However, even with the above-mentioned apparatus, it is difficult to immediately respond to the dew condensation state on the surface of the rotary cylinder and the dew condensation detection result by the dew condensation sensor. That is, if the dew condensation sensor detects that there is no dew condensation on the surface of the rotating cylinder, it is necessary to perform heating until the dew condensation sensor no longer detects dew condensation, during which the device can be used. I could not do it.

The object of the present invention is to detect the dew condensation on the rotary cylinder more accurately, thereby eliminating the restriction on the use of the magnetic recording / reproducing apparatus due to an incorrect judgment of the dew condensation, and also to the magnetic tape and the magnetic recording / reproducing apparatus due to the dew condensation. Is to prevent damage.

[0010]

In order to solve the above problems, in a control method of a magnetic recording / reproducing apparatus having a dew condensation sensor according to the present invention, in a state where the dew condensation sensor (21) detects dew condensation, At the same time, the rotation abnormality of the rotary cylinder around which the magnetic tape is wound is detected, and the tape running operation and the rotation of the rotation cylinder are stopped by detecting the rotation abnormality of the rotation cylinder. If no abnormality is detected in the rotation of the rotary cylinder that winds the magnetic tape, the tape running operation is continued even if the dew condensation sensor operates.

Further, as a method for detecting the abnormal rotation of the rotary cylinder, a cylinder motor (3
Detect the abnormal FG signal value in 2). Further, as a method of detecting the rotation abnormality of the rotary cylinder, the abnormality of the load current value of the cylinder motor (32) that rotationally drives the rotary cylinder is detected.

[0012]

[Operation] If the dew condensation sensor (21) does not detect dew condensation, normal tape running operation is performed. Next, the condensation sensor
When (21) detects dew condensation, the following operation is performed. If the magnetic tape is wound around the rotating cylinder when the dew condensation sensor (21) detects dew condensation, it detects if there is any abnormality in the rotation of the rotating cylinder. Continue the tape running operation. When an abnormality is detected in the rotation of the rotary cylinder, the running of the magnetic tape is stopped and the rotation of the rotary cylinder is stopped.

If the rotary cylinder is not rotating when the dew condensation sensor (21) detects dew condensation, for example, the cassette is not loaded in the magnetic recording / reproducing apparatus, or the cassette is loaded in the magnetic recording / reproducing apparatus. When the cassette is loaded and the operation command such as recording and reproducing is transmitted to the magnetic recording / reproducing apparatus while the magnetic tape is in the loading state, the capstan motor and the rotating cylinder start rotating. At this time, it is detected whether there is an abnormality in the rotation of the rotary cylinder, and if there is no abnormality, the tape running operation is continued as it is. When an abnormality is detected in the rotation of the rotating cylinder,
Stop running the magnetic tape and stop the rotating cylinder.

[0014]

According to the control method of the magnetic recording / reproducing apparatus having the dew condensation sensor having the above-mentioned configuration, when the rotation abnormality of the rotary cylinder is detected while the dew condensation sensor (21) detects the dew condensation, the tape is immediately released. Since the traveling is stopped and the rotation of the rotary cylinder is stopped, damage to the magnetic tape and the magnetic recording / reproducing apparatus is prevented.

Further, even if the dew condensation sensor (21) detects dew condensation, it is not judged as dew condensation unless an abnormality is detected in the rotation of the rotary cylinder. Therefore, the sensitivity of the dew condensation sensor (21) is increased to prevent a slight dew condensation. It can be detected, and more accurate judgment of condensation can be made.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. The first embodiment is an example of detecting the rotation abnormality of the rotating cylinder from the FG signal of the cylinder motor (32), and the second embodiment detects the rotation abnormality of the rotating cylinder from the load current of the cylinder motor (32). This is an example.

[Embodiment 1] FIG. 1 is a schematic circuit diagram of a magnetic recording / reproducing apparatus of the present invention. First, each circuit will be described. The magnetic recording / reproducing apparatus of the present invention comprises a central processing circuit.
(Hereinafter, referred to as “CPU (1)”) performs all control. The CPU (1) has a loading control circuit for controlling a cassette and a magnetic tape loading mechanism.
(5), an operation control circuit (6) for transmitting a user's operation command to the CPU (1), a cylinder motor for rotating the rotary cylinder
Motor control circuit (3) for controlling (32), AND circuit (8),
The tape running control circuit (9) is connected.

The loading control circuit (5) includes a CPU (1)
A cassette loading mechanism (not shown) that inserts and ejects a cassette according to a control command from the cassette, pulls out the magnetic tape from the cassette, and winds the magnetic tape on the rotating cylinder (loading), or the magnetic tape wound on the rotating cylinder. It controls a magnetic tape loading mechanism (not shown) that is stored (unloaded) in the cassette. When the cassette is loaded into the magnetic recording / reproducing apparatus, the cassette loading mechanism loads the cassette and the magnetic tape loading mechanism loads the magnetic tape.
Also, a cassette take-out command is issued from the operation control circuit (6) to C
When it is sent to the loading control circuit (5) via the PU (1), the magnetic tape is unloaded and the cassette is ejected.

The operation control circuit (6) is connected to an operation button (not shown) and sends the operation of the user to the CPU (1).

The motor control circuit (3) rotationally drives the cylinder motor (32) in accordance with a control command from the CPU (1). Cylinder motor transmitted from motor control circuit (3)
A signal for voltage application to (32) is modulated by a PWM circuit (not shown) and transmitted to the cylinder motor (32). The cylinder motor (32) is connected to the rotary cylinder, and the rotary cylinder drives to rotate by the rotation of the cylinder motor (32). The rotation speed of the cylinder motor (32) is detected as an FG signal (a signal obtained by converting the rotation speed of the cylinder motor into a frequency) by an FG detection circuit (31) described later.

The tape running control circuit (9) controls a capstan motor (not shown) for running the magnetic tape at a constant speed according to a recording / reproducing command from the CPU (1).

The AND circuit (8), when the 0 and 1 signals from the comparison circuit A (4) and the comparison circuit B (41) are both 1,
It is determined that there is condensation and it is transmitted to the CPU (1). The details will be described later.

The FG detection circuit (31) includes a cylinder motor (32)
Is converted into an FG signal, and the FG signal is transmitted to a comparison circuit B (41) described later. In normal recording and playback, F
The G signal is about 360 Hz. When magnetic tape is loaded and recording, reproduction or the like is performed while the rotary cylinder is condensed, the rotation speed of the cylinder motor (32) decreases, and the FG signal becomes a small value. In the following, the threshold value of the FG signal at the time of determining the dew condensation is referred to as the FG threshold value.

The sensor control circuit (2) includes a condensation sensor (2
1) and the comparison circuit A (4), and the detected value from the dew condensation sensor (21) is A / D converted and output to the comparison circuit A (4). The dew condensation sensor (21) is composed of a resistance element whose resistance value changes depending on humidity. The resistance value of the resistance element increases as the humidity increases. In the following, the resistance value of the dew condensation sensor (21) at the time of dew condensation determination is used as a resistance threshold value.

The memory (11) is composed of a RAM table, and the FG threshold value and the resistance threshold value are stored in advance.

The comparison circuit A (4) is connected to the sensor control circuit (2), the memory (11) and the AND circuit (8), and the resistance of the dew condensation sensor (21) measured by the sensor control circuit (2). It is determined whether the value exceeds the resistance threshold value set in the memory (11). When the resistance value exceeds the resistance threshold value, the signal 1 is output to the AND circuit (8). If the resistance value is less than or equal to the resistance threshold value, the AND circuit
The signal 0 is output to (8).

The comparison circuit B (41) is connected to the FG detection circuit (31) and the AND circuit (8), and F from the FG detection circuit (31) is connected.
It is determined whether the G signal exceeds the FG threshold value set in the memory (11). When the FG signal is below the FG threshold value, the signal 1 is output to the AND circuit (8). F
When the G signal exceeds the FG threshold value, the signal 0 is output to the AND circuit.

The above-mentioned AND circuit (8) is a comparison circuit A (4).
Also, based on the output signal from the comparison circuit B (41), it is determined whether to stop the tape running operation and the rotation of the rotary cylinder or to continue the operation as it is. When the output signals from the comparison circuits (4) and (41) are both 1, the surface of the rotary cylinder is condensed, and the frictional resistance between the magnetic tape and the rotary cylinder is increased. Judgment is made and the signal is transmitted to the CPU (1). When the output signals from the comparison circuits (4) and (41) are both 0, there is no dew condensation on the rotary cylinder, and the friction resistance between the magnetic tape and the rotary cylinder is also normal. In 1), no signal is transmitted, and operations such as recording and reproducing are continued. Comparison circuit (4) (4
If one of the output signals from 1) is 1 and the other is 0, the measurement error of the dew condensation sensor (21), the magnetic tape and the rotating cylinder are other than the dew condensation (for example, the surface of the magnetic tape is damaged. It is considered that the frictional resistance is increased due to In other words, since the rotating cylinder has no condensation, A
No signal is transmitted from the ND circuit (8) to the CPU (1), and normal recording and reproducing operations are continued.

The operation flow of the first embodiment having the above configuration will be described in detail with reference to FIG. 1 and the flow chart FIG. In the following, the operation when the magnetic recording / reproducing apparatus is powered on will be described with reference to the flowchart of FIG.

When the magnetic recording / reproducing apparatus is in the recording / reproducing state, that is, when the capstan motor and the cylinder motor (32) are rotating (S1), the dew condensation sensor (21) indicates the dew condensation condition of the magnetic recording / reproducing apparatus. Measurement is performed (S2), the measurement result is A / D converted by the sensor control circuit (2), and the resistance value is transmitted to the comparison circuit A (4). In the comparison circuit A (4), the resistance value of the dew condensation sensor (21) is compared with the resistance threshold value of the memory (11) to determine whether the resistance value is above or below the resistance threshold value. Judgment (S3). If the resistance value is greater than or equal to the resistance threshold value, there is a possibility that dew condensation has occurred on the rotating cylinder.
The signal 1 is output to the ND circuit (8) (S5). If the resistance value is less than the resistance threshold value, the rotary cylinder does not have dew condensation, and therefore a signal 0 is output to the AND circuit (8) (S
4).

In parallel with the above operation, the cylinder motor (32)
By detecting the rotation speed of the above as an FG signal by the FG detection circuit (31) (S6), the change in the friction resistance between the rotating cylinder and the magnetic tape is examined. Here, when the rotary cylinder has dew condensation or the magnetic tape is damaged, the friction resistance between the magnetic tape and the rotary cylinder increases when the magnetic tape is loaded or in the recording / reproducing state. And a cylinder motor that drives the rotary cylinder (32)
Appears as abnormal rotation. Therefore, FG detection circuit (31)
The FG signal measured at is transmitted to the comparison circuit B (41).

In the comparison circuit B (41), the FG signal and the memory (1
The FG threshold value stored in 1) is compared (S7). If the FG signal exceeds the FG threshold value, the cylinder motor (32)
Since the rotation speed of has not decreased, a signal 0 is output to the AND circuit (8) (S9). If the FG signal is less than or equal to the FG threshold value, it is considered that the friction resistance with the magnetic tape is increased due to the dew condensation on the rotating cylinder or the damaged magnetic tape. The signal 1 is output to (8) (S8).

When the output signals from the comparison circuit A (4) and the comparison circuit B (41) are both 1 (S10), it is determined that the friction resistance between the rotary cylinder and the magnetic tape is increased due to dew condensation. Since it is considered, a dew condensation detection signal is transmitted to the CPU (1). Based on the signal, the CPU (1) transmits a capstan motor stop command to the tape running control circuit (9) to stop the tape running operation, and the motor control circuit.
A command to stop the application of voltage to the cylinder motor (32) is sent to (3) to stop the rotation of the cylinder motor (32) (S1
1).

Capstan motor and cylinder motor (3
When 2) is stopped, the magnetic recording / reproducing device is operated by the operation control circuit.
No instructions will be accepted except for the cassette removal instruction from (6)
(S12) The recording / reproducing of the magnetic tape is prevented by mistake. Cassette eject command is loading control circuit
When it is transmitted to (5) (S13), the magnetic tape loading mechanism stores the magnetic tape in the unloading state in the cassette, and the cassette loading mechanism ejects the cassette (S14).

When at least one of the output signals from the comparison circuit A (4) and the comparison circuit B (41) is 0, it is determined that the rotary cylinder does not have dew condensation, and normal operations such as recording and reproduction are performed. Continues and returns to S1.

With the above configuration and operation, the dew condensation state of the rotary cylinder, which was determined only by the determination of the dew condensation sensor (21), is detected more accurately by detecting the abnormality of the FG signal of the cylinder motor (32). Can be determined. Conventionally, since the dew condensation is determined only based on the detection result of the dew condensation sensor (21), the use of the magnetic recording device is restricted by an incorrect dew determination. In order to prevent this problem, it was necessary to set a high threshold value for the dew condensation determination of the dew condensation sensor (21), but according to the method of the present invention, the dew condensation is determined in two steps as described above. , The threshold value of the dew condensation sensor (21) at the time of dew condensation determination can be made lower than in the past, and the sensitivity of the dew condensation sensor (21) can be increased, so that the dew condensation can be determined more accurately.

[Embodiment 2] Next, as another embodiment of the present invention, Embodiment 2 will be described in which the rotation abnormality of the rotary cylinder is performed by checking the load current of the cylinder motor (32). In the following description, the same reference numerals as those in the first embodiment indicate the same members as those in the first embodiment, and the description thereof will be omitted.

FIG. 3 is a diagram showing a circuit configuration of the second embodiment. As shown in FIG. 3, the CPU (1) is connected to the loading control circuit (5), the operation control circuit (6), the motor control circuit (3) and the AND circuit (8), and the tape running control circuit (9). ing.

The motor control circuit (3) includes a servo mechanism, applies a voltage to the cylinder motor (32), and
Detect the load current of the cylinder motor (32). If some factor, for example, the surface of the magnetic tape is dirty or damaged, the frictional resistance between the rotary cylinder and the magnetic tape increases. At this time, the servo mechanism detects an abnormality in the load current of the cylinder motor (32) and increases the voltage value applied to the cylinder motor (32) in order to rotate the cylinder motor (32) at a constant rotation speed. .

Normally, if there is an abnormality in the load current detected by the servo mechanism, the applied voltage value is immediately changed to deal with it.
In the case of the present invention, when the measured value of the dew condensation sensor (21) is equal to or higher than the resistance threshold value, it is determined based on the load current detected by the servo mechanism whether or not dew condensation occurs on the rotary cylinder. In the following, the deviation of the load current detected by the servo mechanism from the target value is set to 15%, which is the current threshold value. The current threshold value is stored in the RAM table of the memory (11). In the following, the operation of the magnetic recording / reproducing apparatus when the power is turned on will be described with reference to the flow chart in FIG.
It will be described based on.

Similar to the first embodiment, when the magnetic recording / reproducing apparatus is in the recording / reproducing state, that is, when the capstan motor and the rotary cylinder are rotating (S1), the dew condensation state of the magnetic recording / reproducing apparatus is detected. Measured by (21) (S2),
The sensor control circuit (2) performs A / D conversion, and transmits the resistance value to the comparison circuit A (4). The comparison circuit A (4) compares the resistance value with the resistance threshold value (S3), and outputs the signal 0 or the signal 1 to the AND circuit (8) (S4, S5). The above operation is the same as that of the first embodiment, and will be omitted.

In parallel with the above operation, the motor control circuit (3)
At, measure the load current of the cylinder motor (32) (S
6) The load current value is transmitted to the comparison circuit B (41).

In the comparison circuit B (41), the load current value and the current threshold value are compared (S7). If the load current value is less than the current threshold value, the frictional resistance between the magnetic tape and the rotary cylinder is reduced. Since there is no problem in, and the magnetic tape is running as usual, normal tape loading and recording / reproducing operations are continued. At this time, the AND circuit from the comparison circuit B (41)
The signal 0 is output to (8) (S9).

If the load current value is greater than or equal to the current threshold value,
Since the frictional resistance between the magnetic tape and the rotary cylinder is increasing, the comparison circuit B (41) outputs the signal 1 to the AND circuit (8) (S8).

When the output signals from the comparison circuit A (4) and the comparison circuit B (41) are both 1 (S10), the friction resistance between the rotary cylinder and the magnetic tape increases due to dew condensation. Therefore, the dew condensation detection signal is transmitted to the CPU (1). Based on the signal, the CPU (1) sends a capstan motor stop command to the tape running control circuit (9) to stop the tape running operation, and causes the motor control circuit (3) to move to the cylinder motor (3). Send the command to stop the voltage application to (32) and stop the rotation of the cylinder motor (32).
(S11).

Capstan motor and cylinder motor (3
When 2) is stopped, the magnetic recording / reproducing device is operated by the operation control circuit.
Only a command for taking out the cassette by the cassette loading mechanism from (6) is not accepted (S12) to prevent the magnetic tape from being erroneously recorded / reproduced. A cassette eject command is transmitted to the loading control circuit (5) (S13).
And the magnetic tape loading mechanism puts the magnetic tape in the unloading state and accommodates it in the cassette.
The cassette is ejected by the cassette loading mechanism (S14).

When at least one of the output signals from the comparison circuit A (4) and the comparison circuit B (41) is 0, it is determined that the rotary cylinder has no dew condensation, and normal operations such as recording and reproduction are performed. Continues and returns to S1.

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

The control method of the magnetic recording / reproducing apparatus having the dew condensation sensor (21) of the present invention can be applied to an apparatus for winding a magnetic tape around a rotating cylinder, for example, a VTR, a DAT, a video camera or the like. , It is especially useful for portable video cameras that may be used in places with different temperatures.

In the above embodiment, the circuits are divided in order to explain the circuit configuration in detail. However, as shown by the one-dot chain line in FIGS. It can also be configured with a chip microcomputer (7). Furthermore,
In the above embodiment, when it was determined that there was condensation, the capstan motor and the cylinder motor (32) stopped rotating,
At this time, the magnetic tape may be unloaded at the same time and separated from the rotary cylinder.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram of a magnetic recording / reproducing apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of the first embodiment.

FIG. 3 is a schematic circuit diagram of a magnetic recording / reproducing apparatus according to a second embodiment of the present invention.

FIG. 4 is a flowchart showing the operation of the second embodiment.

FIG. 5 is a flow chart showing the operation of a conventional magnetic recording / reproducing apparatus.

[Explanation of symbols]

 (2) Sensor control circuit (21) Condensation sensor (3) Motor control circuit (31) FG detection circuit (32) Cylinder motor (4) Comparison circuit A (41) Comparison circuit B (8) AND circuit

Claims (3)

[Claims] 1. A method for controlling a magnetic recording / reproducing apparatus by detecting a dew condensation on a surface of a rotary cylinder of a magnetic recording / reproducing apparatus by a dew condensation sensor (21).
In the state where 1) has detected dew condensation, the rotation abnormality of the rotating cylinder that winds the magnetic tape is detected, and when the rotation abnormality of the rotation cylinder is detected, the tape running operation and rotation of the rotation cylinder are stopped. A method of controlling a magnetic recording / reproducing apparatus having a dew condensation sensor, characterized in that the tape running operation is continued if no abnormality is detected in the rotation of the rotating cylinder around the tape. 2. The dew condensation sensor according to claim 1, wherein the abnormal rotation of the rotary cylinder is detected by detecting an abnormal FG signal value of a cylinder motor (32) for rotationally driving the rotary cylinder. A control method for a magnetic recording / reproducing apparatus having the same. 3. The dew condensation sensor according to claim 1, wherein the abnormal rotation of the rotary cylinder is detected by detecting an abnormal load current value of a cylinder motor (32) for rotationally driving the rotary cylinder. A control method for a magnetic recording / reproducing apparatus having the same.