JPH0143378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo mechanism used for head movement and head positioning of a magnetic disk drive.

In order for a magnetic disk drive to correctly write and read data, the magnetic head must be accurately positioned on the target track. High-density magnetic disk devices use a closed-loop servo system to achieve accurate positioning. Disturbances (external forces) are exerted by the force of the machine, gravity, and springs used to return the head to a predetermined position when stopped, resulting in positional deviations depending on the magnitude of the disturbance. Conventionally, two measures have been taken to reduce this positional deviation.

One method is to apply a DC offset voltage to the position control loop to cancel out the disturbance, and the other is to add a circuit for integrating position deviation to the position control loop and increase the DC gain of the servo loop.

The method of applying a DC offset voltage requires adjustment for each device because the amount of positional deviation varies depending on the device, and even if the same device is installed horizontally or vertically, it also needs to be adjusted for each device. It also changes depending on how the position is positioned, so there is a disadvantage that positional deviations that cannot be canceled out remain.

The method of integrating the position error has a time delay in response, and does not operate in speed control mode when moving towards the target track, but starts operation after approaching the target track and enters position control mode, so it is transient. The disadvantage is that the response time is long.

Disturbances also affect the speed signal. Recent magnetic disk drives use a two-phase servo system that uses two position signals with a phase difference of 90 degrees.The two position signals are differentiated and the linear portions are connected to generate a continuous speed signal. Obtainable. The S/N ratio of the speed signal resulting from the position signal differentiation is insufficient to use it as is for speed control, so the current detection signal is usually added to the speed signal resulting from the position signal differentiation and passed through a low-pass filter.
N is improved. The reason why the current detection signal is added is to compensate for the high frequency component of the speed signal being lost in the low-pass filter.

The S/N ratio of the speed signal obtained by adding the current detection signal and passing it through a low-pass filter is improved, but if there is a disturbance, the accuracy deteriorates because the integral of the current is not proportional to the speed. As a result, if the disturbance is large, the actual speed may vary depending on the seek direction in the speed control mode, and the initial speed at which the position control mode is entered varies, causing fluctuations in the transient response of positioning.

The present invention does not require adjustment for each device and can eliminate positional deviation regardless of the installation direction of the device or the position of the head, and can always be used regardless of whether the servo is in speed control mode or position control mode. The first objective is to provide an operable disturbance cancellation circuit.

The second purpose is to eliminate the influence of disturbances on the speed signal.

The present invention provides a head positioning servo mechanism for a magnetic disk device, which has a servo motor that generates a force proportional to the drive current and positions the head on any target track among a plurality of data tracks using a closed loop servo system. The system includes a power amplifier for supplying a drive current proportional to the input voltage to the servo motor, means for detecting the drive current of the servo motor, means for detecting the speed of the servo motor, an integrator, and an error amplifier, A signal obtained by subtracting a disturbance cancellation signal, which is an output signal of the error amplifier, from the current detection signal obtained by the current detection means is input to the device, and the error amplifier calculates the speed estimation signal obtained as the output of the integrator. A disturbance cancellation loop is connected to amplify an error obtained by subtracting the speed signal obtained by the speed detection means, and is configured to add the disturbance cancellation signal to the input of the power amplifier.

The principle of the present invention is briefly described as follows.

If there is no disturbance, the acceleration of the servo motor is proportional to the current, so the speed should be proportional to the integral of the current. The lack of proportionality is thought to be due to disturbances, so adding a current proportional to the error to the motor cancels out the disturbances.

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of the present invention. In Figure 1, reference numeral 1 is a power amplifier with gain G _P
Operates as an [A/V] current amplifier. 2 is a servo motor, and K _F [N/A] is its force constant.
3, 4, and 5 correspond to the movable head part, M is its mass, and 1/S is an integral element. 6 is a current detection means, 7 is a speed detection means, 8 is an integrator, 9 is an error amplifier, and _GC , _GV , _GI /S, and _GD are respective gains. The integral constant G _I of the integrator 8 is set so that its output, the speed estimation signal U ₁ , is at the same level as the speed signal U ₀ that is the output of the speed detection means 7 _.
Adjust to (K _F /M) (G _V /G _C ). 10 is a gain adjustment element when adding the disturbance cancellation signal F, which is the output of the error amplifier 9, to the input of the power amplifier 1. Further, I is the current of the servo motor 2, D is the disturbance, V is the speed, X is the position (displacement), _J1 is the current detection signal, and _J2 is the corrected current detection signal. E is a control signal for bringing the position and velocity closer to target values, and is obtained by conventional technology. The main control to bring the position and speed closer to the target values is performed using the same feedback loop as before (indicated by the dotted line in Figure 1), and only in response to disturbances that disturb the main control, the loop is added to 1 through 9 to 10. The loop works. 7 in an ideal state with no disturbance
The output difference between and 8 is zero, and the disturbance cancellation signal added from 9 to 10 to 1 is also zero,
Block 10 has no effect on the main control.
If there is a disturbance, a difference is created between the outputs of 7 and 8, and a disturbance cancellation signal is generated at the output of 9 and added to the input of the power amplifier 1, so that the main control signal E is no longer affected by the disturbance.

Calculating the relationship between E, D, and V in Figure 1, we find that V
= {EG _P (K _F /M) (1+G _D G _I /S)/S+D/
M/S}/{1+G _D (K _F /M) (G _V /G _C )/S}
becomes.

Here, by substituting the above value for G _I , V=EG _P
(K _F /M)/S+D/M/S/(1+G _D (K _F /
M)(G _V /G _C )/S} is obtained, and the transfer gain from E to V is not affected by the disturbance cancellation circuit, but D is 1/{1+G _D (K _F /M)(G _V / G _C ) /
S}. The DC component of the disturbance is compressed to zero. Furthermore, the band to be compressed can be adjusted by adjusting the gain _GD of the error amplifier.

The disturbance cancellation loop shown in FIG. 1 can be kept operating at all times whether the main control loop is in the speed control mode or the position control mode. What should be noted is that the power amplifier 1 is temporarily saturated in the first half of the normal speed control mode. J ₂ in Figure 1
is calculated as J ₂ = J ₁ - F = EG _P G _C , so it seems that equivalent operation can be achieved by directly inserting E into the input of integrator 8, but in reality, power amplifier 1 saturates. Because of this, F goes awry and doesn't work properly. If J ₂ is created from J ₁ −F as shown in Figure 1, even if power amplifier 1 is saturated, the saturation level of power amplifier 1 in response to main control signal E has been reduced by F/(G _P G _C ). F doesn't go crazy just by becoming it.

Next, regarding the speed detection means, a dedicated tachometer may be used, but a two-phase servo type tachometer may be used.
It is assumed that the system is created by differentiating two position signals. The S/N ratio of the speed signal obtained by position signal differentiation is not very good, but the noise is caused by the gain G _D of the error amplifier 9.
This can be cut by providing low-pass filter characteristics to . Note that in the case of the 1-phase servo system, in the speed control mode, the speed signal can only be obtained discontinuously by position signal differentiation, so it is normal to interpolate by integrating the current detection signal to create a continuous speed signal. be. In this case, the present invention cannot obtain a correct disturbance cancellation signal in the interpolation part, so it is necessary to take measures such as narrowing the effective range of the disturbance cancellation loop, using only position control mode, or installing a separate tachometer. Become.

FIG. 2 shows an example of a circuit embodying the block diagram of FIG. 1 described above. a is a power amplifier, b is a current detection means, and c is a speed detection means. d,
e, f, and g are arithmetic amplifiers, d is a circuit that creates J ₂ −F, e is an integrator, f is an error amplifier that amplifies U ₁ −U ₀ , and g is a circuit that adds F to E. are composed of each.

In Fig. 2, the gain constants in the block diagram of Fig. 1 are, for example, G _P = 1 [A/V], G _C = 1 [V/A],
K _F = 10 [N/A], M = 0.1 [K _g ], G _V = 1 [V/
ms ^-1 ] and determine the circuit constants, the following is an example.

_r1 , _r2 , _r4 , _r5 , _r6 , _r7 , _r9 , _r10 : 10KΩ, _r3 :
1Ω, _r8 : 100KΩ, _r11 : 27KΩ, _C1 : 0.1μF,
_C2 : 0.015μF.

The error amplifier f is given the characteristics of a low-pass filter to suppress noise. The gain of the error amplifier f is determined in consideration of the frequency distribution of the disturbance, the S/N ratio of the speed signal, the stability of the circuit, the accuracy of the servo parameters, etc.

Finally, another effect of the present invention will be explained. FIG. 3 shows a speed signal synthesis circuit that adds a current detection signal to a speed signal obtained by position signal differentiation and passes it through a low-pass filter to create a speed signal with a good S/N ratio. In FIG. 3, V _d is a speed signal obtained by position signal differentiation, J is a current detection signal, and U is a combined speed signal. In the conventional technology, J is J ₁ in Fig. 1, but instead of J ₁ , a modified current detection signal is obtained by subtracting the current consumed for canceling the disturbance.
Using J ₂ has the effect of improving the accuracy of the speed signal.

It is also possible to use the speed signal generated by this speed signal synthesis circuit in the disturbance cancellation loop, but the meaning of the disturbance cancellation signal is that it is a frequency component lower than the cutoff frequency of the low-pass filter of the speed signal synthesis circuit. Limited.

As explained above, the present invention can cancel disturbances by adding a simple circuit to the conventional circuit. Even if the magnitude of the disturbance changes, it automatically follows, so no adjustment is necessary, and since it can be kept in operation all the time, large transient responses will not occur.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 shows an example of a circuit embodying the block diagram of FIG. 1, and FIG. 3 shows an example of a speed signal synthesis circuit whose accuracy is improved by the present invention. In the figure, 1... power amplifier, 2... servo motor, 3, 4, 5... movable head section, 6... current detection means, 7... speed detection means, 8... integrator, 9... error Amplifier, 10...gain adjustment element, E...main control signal, I...drive current of servo motor, D...disturbance (external force), V...speed, X...
...position, J ₁ ...current detection signal, J ₂ ...corrected current detection signal, U ₀ ...speed signal, U ₁ ...speed estimation signal,
F...disturbance cancellation signal, G _P ...gain of power amplifier, G _C ...gain of current detection means, K _F ...
Force constant of servo motor, M... Mass of movable head section, 1/S... Integral element, G _V ... Gain of speed detection means, G _I ... Integral constant of integrator, G _D ... Error amplifier Gain, a...power amplifier, b...current detection means, c...speed detection means, d, e, f,
g...Operation amplifier, _Vd ...Speed signal derived from position signal differentiation, J...Current detection signal or modified current detection signal, U...Synthesized speed signal.

Claims (1)

[Scope of Claims] 1. A head of a magnetic disk device that has a servo motor that generates a force proportional to a drive current and that positions the head on any target track among a plurality of data tracks using a closed-loop servo system. The positioning servomechanism includes a power amplifier for supplying a drive current proportional to an input voltage to the servo motor, means for detecting the drive current of the servo motor, means for detecting the speed of the servo motor, an integrator, and an error amplifier, A signal obtained by subtracting the disturbance cancellation signal, which is the output signal of the error amplifier, from the current detection signal obtained by the current detection means is input to the integrator, and the error amplifier inputs a signal obtained by subtracting the disturbance cancellation signal, which is the output signal of the error amplifier, from the speed estimation signal obtained as the output of the integrator. A head characterized in that it has a disturbance cancellation loop configured to be connected to amplify an error obtained by subtracting the speed signal obtained by the speed detection means, and to add the disturbance cancellation signal to the input of the power amplifier. Positioning servo mechanism. 2. In a speed signal synthesis circuit that adds a current detection signal to a speed signal created by position signal differentiation and passes it through a low-pass filter to obtain a speed signal with a good S/N ratio, the current detection signal as described in item 1 is added instead of the current detection signal. 2. The head positioning servo mechanism according to claim 1, wherein a signal obtained by subtracting a disturbance cancellation signal from the current detection signal is used.