JPH07220417A - Disk device - Google Patents

Abstract

PURPOSE:To accurately detect the traveling accuracy of a pick-up and speedily and stably perform seek control in the seek operation of a disk device such as CD. CONSTITUTION:The period between leading edges of a track cross pulse signal is detected by a first period detection part 37 and that between falling edges is detected by a second period detection part 38 and are output as first and second period detection values. Every time the value of the track cross pulse signal value changes, a period selection part 41 selects the first and second period detection values and then outputs them to a speed conversion part 29. The speed conversion part 29 outputs the speed detection values based on the input period detection values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc device for reproducing information such as a CD.

[0002]

2. Description of the Related Art Optical discs such as audio CDs, CD-ROMs, write-once optical discs, rewritable magneto-optical disc devices, etc. have already been put to practical use, and have been applied to various fields and developed for higher performance. Is actively carried out.

Recently, as a data reproducing device for a computer, a CD-ROM driving device has attracted attention as a center of multimedia. The data reproduction speed of a CD-ROM has been the same as that of a music CD, and it is much slower than that of a hard disk or the like. However, with the increase in application software that handles a large amount of data such as image data, there is an increasing need for speeding up, and in recent years, driving devices having a reproduction speed that is twice the normal speed have become common sense. Furthermore, recently, a drive device capable of reproducing at a quadruple speed has been developed.

The structure of a conventional disk device will be described below with reference to FIGS. 5 to 8 by taking a CD-ROM drive device as an example.

FIG. 5 is a block diagram of a conventional disk device. 1 is an optical disc (CD-ROM), 2 is a spindle motor for rotating the optical disc 1, 3 is an optical pickup for reading information from the optical disc 1, 4 is an objective lens of the optical pickup 3 which faces the optical disc 1, 5 is an objective lens actuator, Reference numeral 6 is an optical sensor for receiving the reflected light from the optical disc 1 through the objective lens 4, 7 is a linear motor for moving the optical pickup 3 in the radial direction of the optical disc 1, 8 is a focus servo control unit, 9 is a tracking servo control unit, 10 Is a seek controller, 11 is a signal processing circuit, 13 is an interface controller, 14 is a spindle motor controller, and 15 is a controller. The operation of the conventional disk device configured as described above will be described.

On the optical disc 1, information tracks on which information signals are recorded are spirally formed, and the track pitch is very small (1.6 μm). Therefore, in order to accurately detect the information signals, It is necessary to control the positioning of the light spot with high accuracy on the rotating optical disc 1. The optical pickup 3 is composed of a mechanism section and an optical section, and the mechanism section has an objective lens 4 for focusing light on the recording surface of the optical disc 1 and a direction perpendicular to the recording surface of the optical disc 1 (hereinafter referred to as focus). The objective lens actuator 5 is integrally provided with an actuator for moving the optical disc 1 in the radial direction (hereinafter referred to as the tracking direction) or in the radial direction (hereinafter referred to as the tracking direction). The optical unit includes various prisms such as a semiconductor laser (not shown) and a sensor. The light from the semiconductor laser is condensed by the objective lens 4 and forms a minute spot on the optical disc 1. The reflected light from the optical disc 1 returns to the objective lens 4 again, and is detected by the optical sensor 6 for detecting the positional deviation of the light spot in the focus direction, the positional deviation in the tracking direction, the information signal recorded on the optical disk 1, and the like. It

From the signal from the optical sensor 6 in the optical pickup 3, a signal processing circuit 11 generates a focus error signal indicating the positional deviation of the light spot in the focusing direction and a track error signal indicating the positional deviation in the track direction, and the objective It is input to the focus servo control unit 8 that controls the position of the lens 4 in the focus direction and the tracking servo control unit 9 that controls the tracking direction, and drives the objective lens actuator 5 so that the light spot follows the target track. The position of the lens 4 is controlled.

Also, when moving greatly between tracks,
The seek control unit 10 controls the linear motor 7 to move the optical pickup 3 to the target track.

On the other hand, the signal of the optical sensor 6 is also used for detecting the RF signal which is an information signal, and after the RF signal is generated by the signal processing circuit 11, it is modulated and demodulated by an internal modulation and demodulation circuit and an error correction circuit. Signal processing such as error correction is performed, and the signal is sent to the host device such as a personal computer through the interface control unit 13.

Since the CD-ROM is the optical disc 1 in which the information signal is recorded on the track at a constant linear density,
In order to correctly reproduce the data written in each track on the optical disc 1 having different radii, the rotation speed of the optical disc 1 must be controlled so that the linear velocity of each track becomes constant. Therefore, the spindle motor control unit 14 controls the spindle motor 2 so that the linear velocity of each track of the optical disk 1 is constant. This rotation control is PLL controlled by reading the data written in the track. As described above, many recent drive devices have two modes of the reproduction speed, that is, the standard speed and the double speed. Therefore, the controller 15 switches between these two modes, and controls the seek controller 10, the spindle motor controller 14, etc. in accordance with these modes.

Here, when the optical disc 1 is used as an external storage device of a computer (not shown), it is necessary to perform the processing operation of the optical disc 1 at a higher speed in order to improve the throughput of the entire system as a data processing speed. For this purpose, it is necessary to perform the seek operation for moving the light spot to the target sector at high speed. This seek method will be described below.

The seek operation is performed by counting the number of tracks which the optical spot has traversed when moving in the tracking direction of the optical disk 1. This will be described with reference to FIG. FIG. 6 is a diagram for explaining the principle of track crossing signal detection in a conventional disk device. 6 (a) is an RF signal waveform at the time of seek operation, FIG. 6 (b) is a waveform of a track crossing signal which is its low frequency component waveform, and FIG. 6 (c) is a threshold value using a comparator. It is the waveform of the track crossing pulse signal binarized by the value. That is, as shown in FIG. 6B, the track crossing signal is a sine wave, and when this sine wave advances by one cycle, it indicates that one track is crossed. Therefore, the sine wave of FIG.
By counting the quantized pulses shown in FIG. 6C, the number of tracks across which the light spot crosses can be known.

In order to move the optical pickup 3 to the target track with high accuracy and high speed, the optical pickup 3
Needs to be moved according to an ideal velocity profile, and in order to realize this ideal velocity profile, the period of the pulse shown in FIG. It is used to control the moving speed of the light spot.

FIG. 7 is a block diagram of a seek controller of a conventional disk device. In FIG. 7, only the elements related to the seek operation among the elements shown in FIG. 5 are shown. First,
The signal processing circuit 11 extracts only the low-frequency component from the RF signal (FIG. 6A) from the optical sensor 6 integrated with the optical pickup 3, and outputs the track crossing signal to the track crossing pulse generator 21 of the seek controller 10. (FIG. 6B) is output. The signal processing circuit 11 also outputs the current sector address signal to the controller 15 and the moving track number calculation unit 19.

In the seek control section 10, a track 21 receives a track crossing signal and outputs a track crossing pulse signal (FIG. 6C) obtained by binarizing the track crossing signal with a certain threshold value as described above. The crossing pulse generator 28 is composed of a timer counter or the like, and receives a track crossing pulse signal and outputs a cycle thereof.
Reference numeral 9 denotes a speed conversion unit that converts the cycle output by the cycle detection unit 28 into a speed and outputs the speed as a current speed detection value. Hereinafter, the cycle detection unit 28 and the speed conversion unit 29 are collectively referred to as a speed detection unit 25. Reference numeral 30 denotes a comparator, which inputs a speed command value output from a target speed generating unit 22 described later and a current speed detection value output from the speed converting unit 29, and calculates a speed difference between the speed command value and the speed detection value. Drive signal 3 to optical pickup 3
2 is output to the drive amplifier 31 that outputs 2.

A sector address signal 19 is input from the signal processing circuit 11, and a target sector command signal indicating a target sector to which the optical pickup 3 should reach is input from the controller 15, and the sector indicated by the sector address signal is changed to a target sector. This is a moving track number calculation unit that calculates the number of tracks up to the target sector indicated by the command signal and outputs a moving track number command signal. 26 is a track counter which inputs a moving track number command signal and a track crossing pulse signal indicating the number of tracks crossed while the optical pickup 3 is moving, and outputs a track difference indicating the number of tracks up to a target sector, and 22 is a track difference. Is a target speed generator that outputs a speed command value corresponding to the distance to the target track to the comparator 30.

The seek control unit 10 in the conventional disk device has the above-mentioned structure, and its operation will be described below.

First, in response to the target sector command signal from the controller 15, the moving track number calculation unit 19 calculates the number of tracks from the current track to the target track where the target sector is located based on the current sector address signal. Then, the moving track number command signal is initialized in the track counter 26.

On the other hand, regarding the state of track crossing during the actual movement of the optical pickup 3, the track crossing signal output from the signal processing circuit 11 is applied to the track crossing pulse generator 2.
The actual moving speed of the light spot is detected by the speed detecting unit 25 using the track crossing pulse signal pulsed by 1, and is output to the comparator 30 as a speed detected value. Then, in the comparator 30, the difference between the speed command value output by the target speed generator 22 and the speed detection value is calculated, and the result is amplified by the drive amplifier 31 to apply the drive signal 32 to the optical pickup 3, The optical pickup 3 is driven. That is, the drive signal 32 of the optical pickup 3 is sent so that the difference between the speed command value and the speed detection value becomes zero,
The movement control of the light spot is performed.

As described above, in the conventional disk device, the speed command value output from the target speed generator 22 and the speed converter 29 are output.
A seek method is used in which the moving speed of the optical pickup 3 is controlled by servo control for sequentially comparing and controlling the speed detection value output by the optical pickup 3 to perform optimum speed control.

However, in the rough seek operation, there is some error in the track movement, and the light spot often stops before the target position or goes too far. In such a case, the optical pickup 3 reads the sector address signal and recognizes the current position of the light spot to perform the movement correction operation to the target track again. This is the operation corresponding to the dense seek. When the target track is entered by this dense seek, the sector address signal is read again to confirm the sector.
Then, the rotation of the target sector is waited until it reaches the light spot as the optical disc 1 rotates, and the target sector is read.

Since the optical disc 1 must be controlled at a constant linear velocity, the spindle motor 2 shown in FIG. 5 must be accelerated or decelerated to the rotational velocity at the seek destination as soon as possible during seek. Normally, the spindle motor control unit 14 performs PLL control of the spindle motor 2 based on the synchronization signal data written in the optical disc 1, but the PLL control is difficult because the synchronization data cannot be read correctly during seeking. Therefore, PLL control is not performed at the time of seek, and the rotation speed at the access destination is given to the spindle motor control unit 14 as a rotation speed command value, so that the rotation speed of the spindle motor 2 becomes a predetermined rotation speed in parallel with the seek operation. Control is performed.

[0023]

However, the above conventional structure has the following problems. That is, in the seek operation, the moving speed of the optical pickup 3 must be accurately detected. In the method of detecting the track crossing pulse shown in FIG. 6, however, an offset is generated in the track crossing signal or the binarization circuit does not operate. The threshold voltage accuracy may be poor, and the ratio between the H (active) section and the L (non-active) section of the track crossing pulse signal (hereinafter referred to as the pulse ratio) may not be equal. In such a case, the first half cycle of the track crossing pulse signal (the cycle when the track crossing pulse signal is H) and the second half cycle of the track crossing pulse signal (the cycle when the track crossing pulse signal is L) are independent of each other. When measured, an error will occur in the speed detected with respect to the actual speed. This will be described with reference to FIG.

FIG. 8 is a diagram for explaining the operation of the speed detecting section when an offset occurs in the track crossing signal of the conventional disk device. In FIG. 8, an offset occurs in the track crossing signal shown in FIG. 6 (b). The operation of the speed detection unit 25 in the case of performing is shown. FIG. 8A shows the waveform of the track crossing signal, and the sine wave is offset slightly downward with respect to the threshold value Vth. 8B is a waveform of the track crossing pulse signal, FIG. 8C is a waveform conceptually showing the operation of the counter circuit in the cycle detector 28, and FIG.
(D) is an output waveform of the speed detector 25.

As can be seen from FIG. 8, when the track crossing signal is offset, the pulse ratio of the track crossing pulse signal becomes uneven (in FIG. 8B, the latter half period of the track crossing pulse signal is long). As a result, it can be seen that the speed detection value varies. As described above, there are problems that the seek operation becomes unstable due to the variation in the speed detection value, the accuracy of seek control deteriorates, and high speed seek cannot be performed.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a disk device capable of accurately detecting the moving speed of a pickup during a seek operation.

[0027]

In order to achieve this object, a disk drive according to a first structure of the present invention comprises a track crossing detecting means for detecting that a pickup has crossed an information track and generating a pulse signal. First cycle detecting means for detecting and outputting a cycle between rising edges of the pulse signal, second cycle detecting means for detecting and outputting a cycle between falling edges of the pulse signal, and first cycle The detection means and the selection means for selecting and outputting the detection value from the second cycle detection means, and the speed conversion means for converting the output of the selection means into the speed value and outputting it.

The disk device according to the second structure of the present invention further comprises track crossing detection means for detecting that the pickup has crossed the information track and generating a pulse signal.
A cycle detecting means for detecting a cycle between edges of the pulse signal and outputting cycle data for each half cycle, and a first half cycle Ta (k− of the pulse signal previously detected by the cycle detecting means.
1) When the second half cycle Tb (k-1) of the pulse signal previously detected by the cycle detecting means and the first half cycle Ta (k) of the pulse signal currently detected by the cycle detecting means are input, Ta '(k ) = Ta (k) / 2α where α = Ta (k−1) / (Ta (k−1) + Tb
(K-1)) is performed to generate a corrected first half cycle Ta ′ (k) of the pulse signal detected this time, and the second half cycle Tb of the pulse signal detected this time by the cycle detection means.
When (k) is input, the correction second half cycle Tb ′ (k) of the pulse signal detected this time is generated by performing the calculation Tb ′ (k) = (Tb (k) + Ta (k)) / 2. And a speed converting means for converting the output of the cycle correcting means into a speed value and outputting the speed value.

[0029]

With the above configuration, even if the half cycle time of the track crossing signal varies during the seek operation, the total cycle time is measured for each half cycle and the speed is detected. The detection error of can be minimized. Further, the speed is detected by correcting the current ratio of the track crossing signal based on the ratio of the track crossing signal in the previous cycle, so that the speed detection error can be minimized.

[0030]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram of a speed detector of a disk device according to an embodiment of the present invention. In FIG. 1, of the speed detecting unit 125, 128 is a cycle detecting unit for inputting a track crossing pulse signal and outputting its cycle, and 29 is a speed converting unit for converting the cycle into speed and outputting a speed detection value. . In the cycle detection unit 128, 37 is composed of a counter or the like, detects the cycle between the rising edges of the track crossing pulse signals, and outputs as the first cycle detection value, the first cycle detection unit, 38. Is a counter or the like, detects a period between falling edges of the track crossing pulse signal, and outputs a second period detection value as a second period detecting unit as a second period detecting unit, and 41 is a first period detecting unit 37. The first cycle detection value output by the second cycle detection unit 3
The second cycle detection value output by 8 is input, and one of the first cycle detection value and the second cycle detection value is selectively selected and output to the speed conversion section 29.

The operation of the disk device configured as above according to the embodiment of the present invention will be described below. The first cycle detecting unit 37 detects the cycle between the rising edges of the track crossing pulse signal generated every time the light spot crosses the track during the seek operation, and detects the cycle between the falling edges of the track crossing pulse signal the second cycle. Part 38
Measure each by. The first cycle detection unit 37 has a first
The cycle detection value is output, and the second cycle detection unit 38 outputs the second cycle detection value. The cycle selection unit 41 selects the first cycle detection value and the second cycle detection value each time the value of the track crossing pulse signal changes, and outputs the selected value to the speed conversion unit 29. The speed conversion unit 29 outputs the speed detection value based on the input cycle.

FIG. 2 is a diagram for explaining the operation of the speed detecting section 125 of the disk device according to the embodiment of the present invention. Figure 2
2A is a waveform of the track crossing pulse signal, FIG. 2B is a waveform conceptually showing the operation of the period detection unit 128, and FIG.
(C) shows the output (cycle) waveform of the cycle selection unit 41. In FIG. 2, the first period detector 37 receives the track crossing pulse signal as shown in FIG.
As shown in the waveform (1) of (b), the up-count operation is started from the initial value each time the rising edge is detected, and when the next rising edge is detected, the value counted up to that point is set as the first cycle detection value. It outputs to the cycle selection unit 41, returns to the initial value, and starts the counting operation again. Similarly, when the second cycle detection unit 38 receives a track crossing pulse signal as shown in FIG. 2A, it detects the falling edge as shown by the waveform (2) in FIG. 2B. When the counting operation is started from the initial value and the next falling edge is detected, the value counted up to that point is output to the cycle selecting unit 41 as the second cycle detection value, the value returns to the initial value and the counting operation is started again.

As shown in FIG. 2C, the cycle selecting section 41 outputs the first cycle detected value when the first cycle detected value is input, and the first cycle detected value is input until the second cycle detected value is input next. Holds the detected value for one cycle. Next, when the second cycle detection value is input, the second cycle detection value is output instead of the first cycle detection value, and the second cycle detection value is held until the first cycle detection value is input next. .

As described above, by detecting the data of one cycle immediately before the edge of the track crossing pulse signal is detected, even if the pulse ratio of the track crossing pulse signal is not equal, the detection error of the cycle detection value is detected. And the variation can be minimized, and thus highly accurate speed detection with a small speed detection error becomes possible.

FIG. 3 is a block diagram of a speed detecting portion of a disk device according to another embodiment of the present invention. In FIG. 3, reference numeral 225 is a speed detection unit, which is composed of a cycle detection unit 28, a cycle correction unit 43, and a speed conversion unit 29. The operation of the disk device constructed as described above in another embodiment of the present invention will be described below. The cycle detecting unit 28 measures the cycle between the rising and falling edges of the track crossing pulse signal and outputs the cycle to the cycle correcting unit 43. The cycle correction unit 43 holds the previously detected cycle detection value for one cycle and half cycle data in the memory, and outputs the correction cycle in which the speed detection value detected this time is corrected to the speed conversion unit 29. .

FIG. 4 is a diagram showing the operation of the cycle correction unit 43 of the disk device according to another embodiment of the present invention. Figure 4
FIG. 4A is a waveform of the track crossing pulse signal, and FIG.
(B) shows the output of the cycle detector 28 and the output of the cycle corrector 43. 4 (b), Ta (k) is the first half cycle of the current pulse, Tb (k) is the second half cycle of the current pulse, Ta (k).
-1) is the first half cycle of the previous pulse, Tb (k-1) is the second half cycle of the previous pulse, Ta '(k) is the first half cycle after being corrected by the cycle correction unit 43, and Tb' (k) is also the same. It is the latter half cycle. Next, the cycle correction unit 43 will be described with reference to FIG.
The operation will be described below. As shown in FIG. 8, even when an offset or the like occurs in the track crossing signal and the pulse ratios of the track crossing pulse signals are not equal, the pulse ratio in the previous cycle and the pulse ratio in this cycle are almost equal. Therefore, the cycle correction unit 43 performs the operation of obtaining the pulse ratio α in the previous cycle and obtaining the estimated value Ta ′ (k) of the current cycle from the detected value Ta (k) of the current cycle, and similarly, The estimated value Tb ′ of the first half cycle is calculated by the detected value Tb (k) of the first half cycle using the pulse ratio α in
The operation for obtaining (k) is performed. That is, as shown in FIG. 4, the first half cycle Ta (k−
1), the second half period Tb (k-1) of the previous pulse and the first half period Ta (k) of the current pulse are input, Ta '(k) = Ta (k) / 2α where α = Ta (k-1) ) / (Ta (k-1) + Tb
(K-1)), the first half cycle T of the correction of the current pulse is performed.
Generate a '(k). That is, the entire period of the current pulse is estimated using the pulse ratio α of the previous pulse and the first half period Ta (k) of the current pulse, and half of the estimated period is set as the corrected first half period Ta ′ (k) of the current pulse. calculate.

When the second half cycle Tb (k) of the current pulse is input, the correction second half cycle of the current pulse is calculated by performing the calculation Tb '(k) = (Tb (k) + Ta (k)) / 2. T
Generate b '(k). That is, the total period T of the pulse now
Half of b (k) + Ta (k) is calculated as the corrected second half cycle Tb ′ (k) of the current pulse. As shown in FIG. 4B, the first half cycle Ta (k) of the current pulse and the second half cycle T of the current pulse, which are data of the half cycle of the track crossing pulse signal.
Although b (k) has a large difference in value, the correction first half cycle T of the current pulse corrected by the cycle correction unit 43
The difference between the values of a ′ (k) and the corrected second half cycle Tb ′ (k) of the current pulse becomes small, and the first half cycle T of the current pulse T
It is an average value of a (k) and the latter half period Tb (k) of the current pulse.

As described above, even when the pulse ratio α of the track crossing pulse signal is not equal, by estimating and outputting the half cycle data of the track crossing pulse signal,
The accuracy of speed detection can be greatly improved.

[0039]

According to the present invention, the first cycle detecting means for detecting the cycle between the rising edges of the pulse signal generated by the pickup and the second cycle detecting means for detecting the cycle between the falling edges of the pulse signal. By independently providing the cycle detection means and by providing the cycle correction unit that corrects the cycle detection value of the current cycle from the data of the first half cycle and the previous full cycle, the speed control during the access operation of the optical pickup is performed. Can be performed with high accuracy, and a seek can be provided at high speed and stable.

[Brief description of drawings]

FIG. 1 is a block diagram of a speed detector of a disk device according to an embodiment of the present invention.

2A is an operation explanatory diagram of a speed detection unit of a disk device according to an embodiment of the present invention; FIG. 2B is an operation explanatory diagram of a speed detection unit of the disk device according to an embodiment of the present invention; Operation explanatory diagram of the speed detection unit of the disk device in the embodiment of the present invention

FIG. 3 is a block diagram of a speed detector of a disk device according to another embodiment of the present invention.

FIG. 4A is a diagram showing an operation of a cycle correction unit of a disk device according to another embodiment of the present invention. FIG. 4B is a diagram showing an operation of a cycle correction unit of a disk device according to another embodiment of the present invention.

FIG. 5 is a configuration block diagram of a conventional disk device.

FIG. 6A is a diagram explaining the principle of track crossing signal detection of a conventional disk device. FIG. 6B is a diagram explaining the principle of track crossing signal detection of the conventional disk device. FIG. 6C is a track crossing signal of the conventional disk device. Illustration of detection principle

FIG. 7 is a block diagram of a seek controller of a conventional disk device.

FIG. 8A is an operation explanatory diagram of a speed detection unit when an offset occurs in a track crossing signal of a conventional disk device, and FIG. 8B shows a case where an offset occurs in a track crossing signal of a conventional disk device. (C) is an operation explanatory diagram of the conventional disk device, and FIG. (D) is an operational diagram of the conventional disk device when the offset is generated. Explanatory diagram of the operation of the speed detection unit when an error occurs

[Explanation of symbols]

 37 First Cycle Detection Section 38 Second Cycle Detection Section 41 Cycle Selection Section 43 Cycle Correction Section

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Wada 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A disc device for reading an information signal recorded on an information track of a disc by a pickup movable in the radial direction of the disc, wherein a pulse signal is detected by detecting that the pickup has crossed the information track. A first track crossing detecting means for generating and detecting and outputting a cycle between rising edges of the pulse signal,
Cycle detecting means, second cycle detecting means for detecting and outputting a cycle between falling edges of the pulse signal, and detection values from the first cycle detecting means and the second cycle detecting means. A disk device comprising: selecting means for selecting and outputting and speed converting means for converting an output of the selecting means into a speed value and outputting the speed value. 2. A disk device for reading an information signal recorded on an information track of a disk by a pickup movable in the radial direction of the disk, wherein a pulse signal is detected by detecting that the pickup has crossed the information track. A track crossing detecting means for generating, a cycle detecting means for detecting a cycle between edges of the pulse signal and outputting cycle data for each half cycle, and a first half cycle Ta (k) of the pulse signal previously detected by the cycle detecting means. -1), when the second half cycle Tb (k-1) of the pulse signal previously detected by the cycle detection means and the first half cycle Ta (k) of the pulse signal currently detected by the cycle detection means are input. , Ta ′ (k) = Ta (k) / 2α where α = Ta (k−1) / (Ta (k−1) + Tb
(K-1)) to generate a corrected first half cycle Ta ′ (k) of the pulse signal detected this time, and a second half cycle Tb (k) of the pulse signal detected this time by the cycle detecting means. ) Is input, the correction second half cycle Tb ′ (k) of the pulse signal detected this time is generated by performing the calculation Tb ′ (k) = (Tb (k) + Ta (k)) / 2. A disk device comprising: a cycle correcting means for outputting; and a speed converting means for converting an output of the cycle correcting means into a speed value and outputting the speed value.