JPH0469347B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a moving speed detection device, and in particular, a position signal for speed detection can only be obtained discretely, such as in a magnetic head of a magnetic disk device. The present invention relates to a method for detecting the speed of a movable member that allows a speed close to an actual value to be obtained even in the case of a moving member.

(b) Prior art and problems Conventionally, analog position signals were mainly used to detect the speed of movable members such as magnetic heads, and the instantaneous value of the moving speed was obtained from the differentiation of continuous positions. However, this method cannot be applied to systems where position signals can only be obtained discretely. On the other hand, in speed detection using digital signal processing, the difference between position and speed can be taken to obtain the average speed within a sample period. However, this method has the disadvantage that when moving at high speed, the difference between the actual moving speed and the actual moving speed increases, making it impossible to obtain an accurate speed.

(c) Object of the Invention An object of the present invention is to provide a moving speed detection device that can reduce speed errors that occur during high-speed movement so that the amount of error is minimized even during low-speed and high-speed movement.

(d) Structure of the Invention The present invention is characterized by comprising a movable member, a motor for moving the movable member, means for detecting a drive current of the motor, and means for detecting the position of the movable member, and means for calculating an average speed within the sampling interval by a differential method from the position of the movable member detected by the position detection means at a first sampling time and a second sampling time after a predetermined sampling interval has elapsed; means for calculating a rate of change in the drive current from the drive current detected by the drive current detection means at the first and second sampling times; and means for correcting the average speed to determine the moving speed of the movable member after an average speed calculation time has elapsed from the second sampling time.

(e) Embodiment of the Invention An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the locus of the movable member, and FIGS. 2 and 3 show its speed. Using these figures, the principle of the present invention will be explained first.

If a position signal indicating the trajectory x=f(t) with respect to time t can be obtained continuously, it is possible to obtain the instantaneous value of the velocity at each time t, but it is possible to obtain the position signal only discretely. If it cannot be obtained, the velocity will be calculated by the difference method. That is, time t _o-1 ,
The positions at t _o , t _o+1 are X _o-1 , X _o , X _o+1 , the actual velocities are V _o-1 , V _o , V _o+1 , and the calculated time t _o is If the average speed is _o , then _o = ∂x/∂t = (X _o −X _o-1 )/(t _o −t _o-1 ). The average speed _o obtained in this manner has conventionally been used as the moving speed (see thick line in FIG. 2) in the period t _o to t _o+1 [section X o to X _{o +1} ]. Therefore, as is clear from the figure, the average velocity obtained in this manner already has a velocity error of V _o - _o . Furthermore, calculating the average speed _o requires calculation time _Δt , so the period in which the average speed _o is used is t _o +Δ _t ~ _{t o+1} +Δ _t , as shown in Figure 3.
The speed error becomes even larger.

In this embodiment, the speed after the calculation time Δ _t has elapsed is estimated, and this is used as the speed during the period from t _o +Δ _t to _{t o+1} +Δ _t . Next, how to obtain the speed after the lapse of _Δt will be explained.

Now, the function representing the trajectory near time t _o is f(t)
Then, using Taylor expansion, the trajectory near time t _o is x = f (t - t _o ) = f (t _o ) + f' (t _o ) (t - t
_o ) + 1/2f'' (t _o ) (t-t _o ) ² +... Therefore, the average speed _o can be expressed as: _o = f (t _o ) - f (t _o-1 )/t _o −t _o-1 = [f(t _o )−{f(t _o )+f′(t _o )(t _o-1 −t _o ) +1/2f″(t _o )×(t _o-1 −t _o ) ² }]/(t _o −t _o-1 ) = f′(t _o )+1/2f″(t _o )(t _o-1 −t _o ) … It can be expressed as: Velocity V _o at time t _o is _Vo = f′(t _o )..., and from the formula, the difference between the actual speed and the average speed is as follows.

V _o − _o = 1/2f″(t _o ) (t _o −t _o-1 )… However, in reality, calculation time △ _t is required to obtain the speed as described above, so this Δ _t must be taken into consideration. The average velocity ′ _o can be expressed as follows.

′ _o =X′ _o −X′ _o-1 /t _o −t _o-1 =f′(t _o +Δ _t ) +1/2f″(t _o +Δ _t )(t _o-1 −t _o )… Above In the formula, f'(t) represents speed.
Assuming that the sampling interval is sufficiently small and the speed is not a function of cubic or higher order, then f′(t _o +Δ _t )=f′(t _o )+f″(t _o )Δ _t +1
/2f(t _o )(Δ _t ) ² …, so ′ _o =f′(t _o )+f″(t _o )Δ _t +1/2f(
t _o )(Δ _t ) ² +1/2f″(t _o +Δ _t )(t _o-1 −t _o ) = V _o +f″(t _o )△ _t +1/2f(t _o )・{
(Δ _t ) ² + Δ _t (t _o-1 − t _o )}… Therefore, the speed error including calculation time is V′ _o −′ _o = 1/2f″(t _o +Δ _t )(t _o − t _o-1 ) = 1/2 {f″(t _o ) + f(t _o ) Δ _t }・ (t _o −t _o1 ) … Substituting the formula into this, we get V′ _o − _o = 1 /2f″(t _o )(t _o −t _o-1 +2Δ _t )
+1/2f(t _o )( _Δt ) ² ... In the above formula, f″(t) is a function of acceleration, and f
(t) is the time rate of change of acceleration. Since this acceleration is proportional to the drive current of the motor that drives the movable member, the value on the right side of the above equation can be determined by knowing the drive current value of the motor and the amount of change in this current over time. .

An embodiment of the moving speed detection device of the present invention based on the above-mentioned principle will be described with reference to FIG.

In the figure, 1 and 2 are analog-to-digital converters (A/D converters), 3, 4, 5, and 10 are I/O ports, 6 is a clock generation circuit, and 7
is a central processing unit (CPU), 8 is a random access memory (RAM), 9 is a read-only memory (ROM), 11 is a digital-to-analog converter (D/A converter), 12 is a movable member, and 13 is a motor , 14 is a drive current detection section for the motor 13, 15
is a position detection section of the movable member 12.

The drive current of the motor 13 that moves the movable member 12 is detected by the drive current detector 14 at every predetermined sampling time, and an analog signal corresponding to the drive current value is sent to the A/D converter 1.
This analog signal is converted into digital data by the A/D converter 1. On the other hand, at each sampling time, the position detecting section 15 detects the position of the movable member 12 and sends out an analog signal indicating the position, and this signal is converted by the A/D converter 2 into corresponding digital data.

The CPU 7 reads out the position data and drive current data via the I/O ports 4 and 3, and calculates the average speed _o and the speed correction value. When the motor 13 uses a voice coil type driver, the speed correction value is determined by α representing the acceleration, M representing the mass of the moving part, I representing the drive current at sampling time t _o , and B representing the motor coefficient. Then, there is a relationship α=f″(t _o )=B/MI(t _o )..., and the above f(t _o ) is f(t _o )≒f″(t _o )−f″(t _o-1 )/t _o −t _o-1 ... Therefore, the first term on the right side of the equation can be found from the equation, and the second term of the same equation can be found from the equation. Therefore, the sampling time interval and calculation time are If predetermined, the correction value can be determined as a function of the current value and the amount of current change.

Therefore, correction values for the above-mentioned current value and current change amount are calculated in advance, and this table is stored in the ROM 9 together with the correction program. CPU7
reads the motor drive current data and position data according to the above program, determines a correction value by referring to the above table, and sends a signal indicating the speed corrected using this correction value to I/O port 5 and D/A.
Output via converter 11.

As described above, according to this embodiment, at time t _o +Δ _t
The velocity V′ _o (see FIG. 3) can be output as the velocity of the movable member 12. Therefore, it becomes possible to control the movement of the movable member 12 using a value much closer to the actual speed than in the past.

The present invention can be used not only to control the position of the magnetic head of a magnetic disk drive, but also to control the position of any movable member.

(f) Effects of the Invention As explained above, the present invention makes it possible to detect the moving speed of a movable member with extremely high accuracy even when moving at high speed.

[Brief explanation of the drawing]

1 to 3 are diagrams for explaining the principle of the present invention, and FIG. 4 is a block diagram showing the main parts of the system configuration of an embodiment of the present invention. In the figure, 1 and 2 are analog-to-digital converters (A/D converters), 3, 4, 5, and 1
0 is an I/O port, 6 is a clock generation circuit, 7 is a central processing unit (CPU), 8 is a random access memory (RAM), 9 is a read-only memory (ROM), and 11 is a digital-to-analog converter ( D/A converter), 12 is a movable member, 13 is a motor, 14 is a drive current detection section for the motor 13, 15
is a position detection section of the movable member 12.

Claims (1)

[Claims] 1. A movable member 12, a motor 13 for moving the movable member 12, a drive current detection means 14 for the motor 13, and a position detection means 15 for the movable member 12. , and the position detection means 15
means 7 for calculating an average speed within the sampling interval by a differential method from the position of the movable member 12 detected at a first sampling time and a second sampling time after a predetermined sampling interval has elapsed; and means 7 and 9 for calculating a rate of change in the drive current from the drive current detected by the drive current detection means 14 at a second sampling time; and a calculation time for the drive current value, its rate of change, and the average speed; means 7 for calculating the moving speed of the movable member 12 after the average speed calculation time has elapsed from the second sampling time by correcting the average speed using .