JPH03237667A - Magnetic head positioning controller of magnetic disk device - Google Patents

Abstract

PURPOSE:To highly precisely execute a seeking operation and a track following operation by correcting an external force compensating quantity which is previously measured, obtained and stored by individual types for cancelling external force added to a magnetic head positioning device to a value adjusted to external force which is actually operated to the positioning device. CONSTITUTION:When the mechanical characteristic of the magnetic head positioning device 6 changes owing to the influence of a temperature, external force fluctuates. For cancelling the influence of external force, an external force compensating value stroed in an external force compensating value table means 9 in accordance with the track number of the magnetic disk 1 is added to a manipulated variable by feed forward. The external force compensating value is that to which the values obtained by previous measurement by the individual types of the magnetic disk devices and for respective tracks 3 are stored. A controller corrects the external force compensating value stored in the table means 9 by adjusting it to actual external force added to the positioning device 6 of the magnetic disk device in a period when there is no operation command from a host device. Thus, the seeking operation and the track following operation are highly precisely executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic head positioning control device that can accurately compensate for external forces acting on a magnetic head positioning mechanism in a magnetic disk device.

[Prior Art] Conventional magnetic head control devices for magnetic disk devices are disclosed in Japanese Patent Laid-Open Nos. 61-120385 and 1982-14.
No. 9082, JP-A-62-140279, JP-A-62
It is described in, for example, Japanese Patent No.-217471. These publications describe that the external force acting on the magnetic head positioning mechanism is measured and stored in advance by some means, and that the corresponding amount is compensated in the magnetic head positioning control device.

[Problem to be solved by the invention] However, the external force is unique to each magnetic disk device, and has a different value for each track of the magnetic disk.
Furthermore, although it is important that the compensation value varies with the operating time, the above-mentioned conventional technology uses an external force compensation value that is determined and stored in advance for each model, and this is applied to the head positioning mechanism of each magnetic disk drive. Since the correction is not made in accordance with the actual external force applied to the magnetic head, there is a problem in that the amount of deviation between the magnetic head and the magnetic disk track (track deviation amount) cannot be sufficiently reduced. SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic head positioning control device that can accurately compensate for external forces that are unique to individual magnetic disk drives, take different values for each track, and further fluctuate over operating time. .

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a magnetic head positioning control device as set forth in each claim.

[Function] In the present invention, in order to cancel the external force applied to the magnetic head positioning mechanism, the external force compensation amount, which has been measured and stored in advance for each model, is applied to the magnetic head positioning mechanism of each individual magnetic disk drive at that time. By correcting the value to match the external force actually acting on the positioning mechanism, subsequent seek operations and track following operations can be executed with high precision in the respective magnetic disk drives.

[Implementation example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall configuration of a magnetic head control device for a magnetic disk drive according to this embodiment. 1 is a magnetic disk, 2 is a magnetic head, and 3 is a plurality of concentric tracks formed on the magnetic disk 1 on which magnetic recording signals are recorded. Since a signal corresponding to the deviation d between the magnetic head 2 and the center of the track 3 is generated in the magnetic head 2, this signal is demodulated by the demodulation circuit 4 and becomes a signal corresponding to the amount of track deviation. Reference numeral 5 denotes a following filter that calculates and outputs a manipulated variable for driving and controlling the magnetic head positioning mechanism 6 in a direction that makes the amount of track deviation zero in a track following operation that causes the magnetic head 2 to follow a target track. , - A lag-lead filter is often used for aggregation. This operation amount is added to an external force compensation amount (described later) by an adding means 8A, amplified by a power amplifier 7, and then transmitted to a positioning mechanism 6 having a movable part via a flexible printed wiring (hereinafter referred to as FPC). be done.

Since the FPC is generally a flexible flat cable made of resilient plastic, it exerts an external force F on the positioning mechanism 6. In addition, during operation, there are external forces caused by wind and retract springs generated due to the high speed rotation of the magnetic disk.

Such an external force becomes a major factor that inhibits the track following operation that causes the magnetic head 2 to follow the target trunk with high precision and the seek operation that moves the magnetic head 2 to the target track at high speed.

This external force differs depending on the individual magnetic disk drive, and even in the same magnetic disk drive, it varies depending on the track position.

For example, since FPCs etc. have variations in their characteristics, the external force exerted by them is unique to each individual magnetic disk drive, and the amount of deflection of the FPC changes when the track position changes, so the external force exerted by FPCs varies from track to track. Becomes a value.

Furthermore, if the positioning mechanism 6 or the FPC has mechanical characteristics that change due to temperature, the external force will vary with operating time.

In order to cancel the influence of this external force, in this embodiment, the external force compensation value stored in the external force compensation value table means 9 is added to the manipulated variable by feedforward according to the track number of the magnetic disk. This external force compensation value must be measured in advance for each magnetic disk drive model and for each track or predetermined plurality of tracks using a force measuring device such as a spring scale before undergoing the modifications described below. The values obtained are stored in memory. Generally, the external force does not change suddenly and greatly depending on the track position, so it is not necessarily necessary to store the above external force compensation value for each track, but for multiple tracks at an appropriate predetermined interval. It is sufficient to do so, and it saves memory. In this case, for a track that is not stored in the table 9, the external force compensation value can be determined with high accuracy by interpolation from the external force compensation values for the tracks before and after it, for example.

By the way, as mentioned above, the actual magnitude of the external force varies depending on the magnetic disk device, and also changes depending on the track position and further over time, so in the control device of this embodiment, The external force compensation value stored in the external force compensation value table means 9 in advance is stored in the second
Correct it by following the steps shown in the figure below.

First, during the above period, the track position selection means 10 is automatically given the number of the track whose external force compensation value is to be modified, that is, the number of the track whose external force compensation value is stored in advance in the table 9. The track is selected and the magnetic head 2 is moved to the track by the track moving means 11. This corresponds to a normal seek operation, and the switch S is closed to the seek side. 30 is a feedback line for seek operation. In this seek operation, while the magnetic head 2 is being moved to the track, the external force compensation value corresponding to the track is read from the external force compensation value table means 9, and the signal from the track position moving means 11 is read out in the adding means 8B. By applying the force in a feedforward manner, the influence of the external force on the seek operation is compensated for.

After moving to the track, the switch S is switched from the seek side to the following side, and the following operation is performed on the selected track by the above-mentioned following operation loop. In this following operation as well, the external force compensation value corresponding to the track in question is read out from the external force compensation value table means 9 and added to the manipulated variable from the following filter 5 in a feedforward manner in the adding means 8A. In this way, the positioning mechanism 6 is controlled by the control operation amount obtained by adding the external force compensation value to the operation amount to perform the track following operation.

While performing this track following operation, the sampler 12 samples the amount of track deviation from the demodulation circuit 4 in response to a sampling command from the decision control means 16, and using this sampled value, the average value calculation means 13 calculates the amount of track deviation for a predetermined period of time. Find the average value of the amount of track deviation within. The reason why sampling is performed here is to reduce the effort of calculating and finding an average value from the amount of positional deviation of the magnetic disk several rotations in the case of the dedicated servo system. However, in the case of a sector servo system in which the amount of track deviation is originally obtained only intermittently, the sampler 12 is not necessary.

When the obtained average value is within a predetermined range close to zero, external force compensation is being performed accurately, but when this value deviates significantly in the positive or negative direction, the external force compensation value is insufficient. Either there is too much, or there is too much.

In this case, the correction value of the external force compensation value corresponding to the output value from the average value calculation means 13 is calculated by the correction value calculation means 14, and the correction value is read out from the external force compensation value table means 9 in the adding means 5. A new external force compensation amount obtained by this addition is added to the operation amount from the following filter 5 by feedforward in the adding means 8A.

For convenience of explanation, the sign of the amount of track deviation and the sign of the amount of correction of the external force compensation value corresponding thereto are determined as shown in FIG.

When the track deviation amount reaches a value within a predetermined range close to zero, the corrected value at that time is added to the external force compensation value for the track in question from the table means 9, and the resulting value is used as the final external force compensation for the track in question. None, the content related to the track in the external force compensation value table 9 is rewritten to the above-mentioned final external force compensation value.

The above operations and processing are performed for each track whose external force compensation value is stored in advance in table 9, and the contents of table 9 are used as the final external force compensation obtained in the same manner as above for each track. Rewrite to value. The above sequence is performed according to instructions from the decision control means 16.

FIG. 9 shows that by rewriting the table of the corresponding track in the external force compensation value table means 9 to the final external force compensation value as described above, the contents of the external force compensation value table means are changed to the values before correction (indicated by the solid line). This is an example of how the value is rewritten to the corrected value, that is, the final external force compensation value (indicated by a broken line). This rewritten final external force compensation value is used in subsequent track following operations and seek operations when the magnetic disk device is used. This makes it possible to reduce the amount of track deviation not only in the following operation but also in the seek operation when the magnetic disk device is used.

Various procedures can be considered to obtain the correction value for converging the average value of the track deviation amount within a predetermined range close to zero in Fig. 3, and one method is shown in Fig. 4 (a).
b) and (c), and another method is shown in FIG. These figures extract and explain only the procedure for determining the correction value, and the explanation of other procedures in FIG. 2 is omitted.

Figures 4 (a), (b), and (C) show a procedure based on the so-called dichotomous method. In the diagram, P is plus, M is minus, 2
means zero or close to zero.

FIG. 4(a) shows the procedure when track following control is performed using the external force compensation value read from Table 9. If the average value of the track deviation amount is negative, then the fourth A correction value is obtained by the procedure shown in FIG. If the average value of the track deviation amount is positive, then from the following figure 4 (
Obtain the corrected value using the procedure shown in C). If the average value of the track deviation amount is within a predetermined range close to zero, the value read from the external force compensation value table means 9 is directly used as the final value of the external compensation value.

FIG. 4(b) shows a case where the initial average value of the track deviation amounts in FIG. 4(a) is negative. First, the maximum value of the correction values is selected as the correction value, and the sign of the average value of the amount of track deviation is checked using the procedure shown in FIG. If the average value of the track deviation amount is negative, it is inconvenient to increase the correction value any further, so this maximum value is set as the final correction value. On the other hand, if the average value of the track deviation amount is positive, the correction value is set to the maximum value x 1/2.
and adjust the sign of the average value of the track deviation amount.

When the average value of the track deviation amount is negative, the maximum value x (
1/2+1/4) and check whether the average value of the track deviation amount is positive or negative. In addition, if the average value of the track deviation amount is positive, the maximum value X (1/2-1/4) is selected again.
Check whether the average value of the track deviation amount is positive or negative. Below, the same figure (
According to the procedure shown in b), the correction value is repeatedly selected until the average value of the amount of track deviation converges within a predetermined range close to zero. According to this method, the correction value is obtained using a predetermined maximum value as a reference and a strict rule, so it is easy to implement. In addition, if you decide the predetermined range appropriately, this repeated procedure will definitely be completed.
The final correction value can be determined.

FIG. 4(C) shows a case where the initial average value of the track deviation amounts in FIG. 4(a) is positive. In this case, the correction value is first selected as the minimum value of the correction values, and the sign of the average value of the track deviation amount is adjusted by the same procedure shown in FIG. Hereinafter, the procedure for determining the correction value is the same as in the case of FIG. 4(b).

Next, FIG. 5 is a flowchart showing another method. In the same manner as in the previous example, the magnetic head 2 is moved to a predetermined track, and then the external force compensation value corresponding to this track is read out and added to the manipulated variable from the following filter 5 in a feedforward manner to perform the track following operation. Have them do it. At this time, the amount of track deviation is sampled by the sampler 12, and the average value of the amount of track deviation within a predetermined time is determined. When the obtained average value is within a predetermined range close to zero, external force compensation is being performed accurately, but if this value deviates significantly in the positive or negative direction, the external force compensation value is insufficient. If there is or is too much,
Depending on the direction of the deviation, the external force compensation value is sequentially decreased or increased by one unit so that the average value falls within a predetermined range close to zero. Assuming that the relationship between the sign of the track deviation amount and the correction amount of the external force compensation value is determined as shown in Fig. 3, when the average value of the track deviation amount is positive, the external force compensation value is decreased by l unit, When the average value of the track deviation amount is negative, the external force compensation value is increased by one unit. If the predetermined range is appropriately determined, this iterative procedure will always be completed and the final corrected value can be obtained. If the control circuit is a digital controller such as a microcomputer, the lower limit of the unit of external force compensation value is determined by the minimum output of the DA converter.
It can be selected depending on the required accuracy of the external force compensation value.

Compared to the previous method, this method has the advantage of simpler programming and fewer errors, but there is a concern that it takes longer to determine the final correction amount. However, since the amount of correction of the external force compensation value usually varies within a range of several times the minimum output of the DA converter, it does not take much time.

FIG. 6 is a flowchart showing one method for keeping the average value of the amount of track deviation within a predetermined range close to zero without repeating the procedure. In the same way as in the previous example, the magnetic head 2 is moved to a predetermined track on the magnetic disk 1, and the external force compensation value corresponding to this trunk is first read out and added to the manipulated variable from the following filter 5 in a feedforward manner. Perform track following operation. At this time, the amount of track deviation is sampled by the sampler 12, and the average value of the amount of track deviation within a predetermined time is determined.

If the functional relationship between the average value of the track deviation amount and the correction amount of the external force compensation value is determined quantitatively in advance in the form shown in Figure 3, the external force compensation value can be corrected immediately from the average value of the track deviation amount. You can find the quantity.

This method has the advantage that it does not require repeated steps and can be completed in a short time compared to the previous method, but it requires time and effort to obtain the relationships shown in Figure 3 in advance.
The drawbacks are that the accuracy may deteriorate. Therefore, it is advisable to combine this method with the method shown above.

FIG. 7(a) shows the overall configuration of another embodiment of the present invention. In FIG. 1A, the same numbers as in FIG. 1 indicate the same parts. FIG. 7(b) is a chart showing a method of correcting the external force compensation value in this embodiment. As in the previous embodiment, a track is selected by the track position selection means 10, and the magnetic head 2 is moved to the selected track by the track position moving means 11. Next, read out the external force compensation value corresponding to this trunk from the external force compensation value table means 9,
It is added to the manipulated variable from the following filter 5 in a feedforward manner, and the track following operation is performed by the control loop described above. These sequences are performed by the decision control means 19. At this time, the amount of track deviation (that is, the amount of trunk deviation assuming that there is no external force) based only on the control operation amount, which is the sum of the operation amount output from the following filter 5 and the current external force compensation value, is calculated. The theoretical value is calculated by the external force compensation theoretical value calculating means 17. To explain this, the above operation amount + external force compensation value, that is, the control operation amount corresponds to the force acting on the head positioning mechanism 6 when it is assumed that there is no external force, so this can be expressed as By performing double integration or approximate double integration at , the theoretical value of the head position, that is, the amount of track deviation, assuming that there is no external force, can be obtained.

Here, S is Laplace's operator, A is a constant, and A2 is a constant determined corresponding to the positioning mechanism system. However, in reality, an external force is acting; if this is not -M with the external force compensation value, a deviation will occur between the theoretical value of the amount of track deviation and the actual amount of track deviation.

Based on this deviation, a correction value for the external force compensation value is obtained in the correction value calculation means 18, and in the addition means 15, this correction value is added to the external force compensation value read from the external force compensation value table means 9, and the correction value is The operation amount from the ing filter 5 is added. When the deviation between the theoretical value of the amount of track deviation and the actual amount of track deviation becomes a value within a predetermined range close to zero, the external force compensation value to which the correction value at that time is added is set as the final external force compensation value, Rewrite the contents of the external force compensation value table means 9 to this.

This rewritten final external force compensation value is used in subsequent track following operations and seek operations.

Note that the amount of correction of the external force compensation value can be simply determined by adding a predetermined gain to the deviation between the theoretical value and the actual value of the amount of track deviation.

FIG. 8(a) shows the overall configuration of another embodiment of the present invention. In FIG. 8(a), the same symbols as in FIG. 1 indicate the same or corresponding parts. FIG. 8(b) is a chart showing a method of correcting the external force compensation value in this embodiment. As in the previous embodiment, the track position selection means 10 selects a track, and the trunk position moving means 1 moves the magnetic head 2 to the selected track. Next, the external force compensation value corresponding to this track is read out from the external force compensation value table means 9 and added to the operation amount from the following filter 5 in a feedforward manner, and the track tracking operation is performed by the aforementioned control loop. Based on the actual amount of track deviation detected at this time.

The theoretical value of external force compensation is calculated from the theoretical value of the actual force acting on the head positioning mechanism 6 (the sum of the external force and the control operation amount obtained by adding the external force compensation value to the operation amount output from the following filter 5). The calculation is performed in the means 20. To explain this, the actual amount of track deviation corresponds to the position of the head positioning mechanism 6 with respect to the track under the force that actually acts, so this is differentiated by a double differential or a double near 4g with respect to time. By this, the actual force acting on the head positioning mechanism 6, that is, the control operation amount obtained by adding the external force compensation value from the external force compensation value table means 9 to the operation amount output from the following filter 5, and the external force. The theoretical value of the sum is found. Here, S is Laplace's operator, B is a constant, and B2 is a constant determined corresponding to the positioning mechanism. Based on the deviation between the above theoretical value and the control operation amount (operation amount from the following filter 5 + external force compensation value from the external force compensation value table 9) output from the addition point 8A, the correction value calculation means 21 calculates the external force Find the correction value of the compensation value. This modified value is added to the external force compensation value read from the external force compensation value table means 9 in the addition means 15 in response to a command from the decision control means 22, etc., and this modified external force compensation amount is added to the manipulated variable by feedforward. It will be done.

Simply, the deviation can be multiplied by a predetermined gain to obtain the correction amount of the external force compensation value.

As a result of this correction, when the deviation of the amount of track deviation becomes a value within a predetermined range close to zero, the external force compensation value corrected by the correction value at that time is set as the final external force compensation value, and the external force compensation value table means 9 Rewrite the table to this,
This rewritten external force compensation value is used in subsequent track following operations and seek operations.

As described above, in each of the embodiments described above, the table of the external force compensation value table means 9 is successively rewritten with new final external force compensation values, and the table is graphed as shown in FIG. 9. In the figure, the horizontal axis is the track position, and t-t0 indicates the track position after correcting the external force compensation value. - Since the external force changes in a nearly linear manner over the entire track within the shell, it is not necessarily necessary to set the external force compensation value finely for each track, and from the point of view of reducing the capacity of the external force compensation value table means 9. It is a good idea to store it as a step-wise function for multiple tracks. The vertical axis is the external force compensation value, the solid line shows the value before correction, and the broken line shows the value after correction. In this way, it is presumed that the amount of correction is often determined with a constant width and a constant slope.

For tracks where external force compensation values are not stored,
The external force compensation value may be determined by interpolation.

FIG. 10 is a diagram showing the overall configuration when positioning the magnetic head 2 with respect to a target track when using a magnetic disk using this rewritten external force compensation value table, Only the necessary parts of FIG. 7(a) and FIG. 8(a) are shown. In use, when the target track number is supported, the switch S is first switched to seek, and the track positioning movement means 11 and seek feedback line 30 perform a seek operation to move the magnetic head 2 to the target trunk. The external force compensation value from the external force compensation value table means 9 is added in a feedforward manner to the signal from the track position moving means 11 by the addition means 8B in accordance with the trunk passing through during this seek operation, and the external force compensation value in the seek operation is can compensate for the effects of After moving to the target trunk, the switch S switches from seek to following, and in the target trunk, the head performs a following operation using the operation amount from the following filter 5 so that the head follows this. In the following operation, the external force compensation value from the external force compensation value table 9 is added to the operation amount from the following filter 5 by the adding means 8A in a feedforward manner according to the track concerned, so that the influence of the external force on the following operation is compensated. be able to.

In the above explanation, in order to specifically explain the control device, functions are divided into blocks. It is a good idea to realize this by In this case, each block becomes a digital operation. Therefore, it is necessary to convert the integral and differential elements shown in FIGS. 7(a) and 8(a) into those expressed by discrete-time operators and constants. This - example 11th
The figure shows block 17 in FIG. 7(a) converted into discrete time operators and constants. A similar expression can be made for FIG. 8(a).

Note that the contents of the external force compensation value table that have been modified and rewritten as described above may be further modified and rewritten in the same manner as described above, if necessary, when the magnetic disk drive is not used thereafter. Of course, by repeating the update of rewriting to the final external force compensation value, it is possible to perform compensation according to the external force that changes over time.

[Effects of the Invention] As described above, according to the present invention, the external force compensation value measured in advance in any of the magnetic disk drives and stored in the external force compensation value table means is unique to each magnetic disk drive, and The final external force compensation value is corrected according to the external force that changes during each operation and changes during the operation time, and this corrected final external force compensation value is added to the manipulated variable by feedforward to control the positioning mechanism, so the amount of track deviation can be sufficiently reduced. It is possible to improve the control performance of the seek operation, shorten the access time, and improve the track following accuracy.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of a magnetic head control device for a magnetic disk device according to the present invention, FIG. 2 is a flowchart for explaining the control method and functions of the control device according to the embodiment, and FIG. FIG. 4(a) is a diagram showing the relationship between the amount of track deviation and the external force compensation value. (b) and (C) are diagrams showing the procedure for calculating the amount of modification of the external force compensation value in Figure 2, and Figures 5 and 6 respectively show different specific examples for modifying the external force compensation value. FIG. 7(a) is a diagram showing the overall configuration of another embodiment of the present invention, FIG. 7(b) is a diagram showing a flow for determining the correction value of the external force compensation value, and FIG. FIG. 8(a) is a diagram showing the overall configuration of still another embodiment of the present invention, FIG. 8(b) is a diagram showing the flow for determining the correction value of the external force compensation value,
The figure shows a graph of the external force compensation value table.
FIG. 10 is a diagram showing a configuration when performing a seek operation and a following operation using a rewritten external force compensation value table, and FIG. I1 is a diagram showing an example of block 17 in FIG. 7(a). 1...Magnetic disk 2...Magnetic head 3...
Trunk 4...Demodulation circuit 5...Following filter 6...Positioning mechanism 7...Power amplifier 8A
, 8B...Addition means 9...External force compensation value table means 10...Track position selection means 11...Track position moving means 12...Sampler 13...Average value calculation means 14.18, 21. ... Correction value calculation means 15 ... Addition means 16.19, 22 ... Decision control means 17.20 ... External force compensation theoretical value calculation means Fig. 2 (1 other person) Fig. 3 Fig. (a ) Figure 5 Figure 7 (b) Figure 8 (b) Figure Figure 1

Claims (1)

[Scope of Claims] 1. In a magnetic head positioning control device of a magnetic disk device that controls a magnetic head positioning mechanism that positions a magnetic head on an arbitrary selected track among a plurality of tracks of a magnetic disk, a detection means for detecting the amount of track deviation between the magnetic head positioning mechanism, a means for calculating an operation amount for a track following operation from the detected amount of track deviation, and a means for compensating for the influence of external force acting on the magnetic head positioning mechanism. external force compensation value table means storing external force compensation values for a plurality of specific tracks; and a control operation amount represented by the sum of the external force compensation value retrieved from the external force compensation value table means for the selected track and the operation amount. means for inputting the information into the magnetic head positioning mechanism to perform a track following operation on the selected track; and selecting the specific track whose external force compensation value is stored in the external force compensation value table means. The effect of the external force actually acting on the magnetic head positioning mechanism at that time is determined from the amount of track deviation detected during the period when the track following operation is performed as described above for the specified track (hereinafter referred to as the specified period). A magnetic disk comprising: correction value calculation means for calculating a final external force compensation value for compensating for the external force; and means for rewriting the external force compensation value stored in the external force compensation value table into the final external force compensation value. The device's magnetic head positioning control device. 2. The correction value calculation means calculates an average value within a predetermined time of the amount of track deviation detected during the specific period, and when this average value deviates from a predetermined small range, the correction value calculation means Using a control operation amount expressed as the sum of the operation amount and a corrected external force compensation value obtained by increasing or decreasing the external force compensation value for the selected specific track read from the means by a predetermined amount depending on the direction of deviation. The method of repeatedly performing track following by sequentially decreasing the predetermined amount of increase/decrease described above, and when the average value converges within the predetermined small range, the modified external force compensation value is the final external force compensation. 2. A magnetic head positioning control device for a magnetic disk drive according to claim 1. 3. The magnetic head positioning control device for a magnetic disk device according to claim 2, wherein the predetermined increase/decrease amount is repeated as the same constant unit amount instead of being made smaller sequentially. 4. The correction value calculation means calculates an average value within a predetermined time of the amount of track deviation detected during the specific period, and calculates a final external force compensation value based on a predetermined functional relationship with respect to this average value. 2. The magnetic head positioning control device for a magnetic disk device according to claim 1, wherein: 5. The correction value calculation means calculates the amount of track deviation detected in the specific period from the deviation between the amount of track deviation detected in the specific period and the amount obtained by double integrating or approximate double integrating the control operation amount in the specific period with respect to time. 2. The magnetic head positioning control device for a magnetic disk device according to claim 1, wherein the device calculates a final external force compensation value. 6. The correction value calculating means calculates a final external force compensation value from the deviation between the control operation amount and an amount obtained by double differentiating or approximate double differentiating the amount of track deviation detected during the specific period with respect to time. 2. The magnetic head positioning control device for a magnetic disk device according to claim 1, wherein the magnetic head positioning control device calculates the following.