Title: Method and apparatus to measure disk drive head load/unload velocity
Abstract: One embodiment of the present invention is an apparatus to provide a measure of disk drive head velocity in a disk drive wherein movement is produced by a disk drive motion mechanism that includes a coil, which apparatus includes: (a) a controller that outputs one or more digital signals that are applied as input to a first component, and in response, the first component outputs a reference voltage; (b) a second component, responsive to voltage output across the coil and the reference voltage, outputs a measure of a difference between the coil voltage and the reference voltage; and (c) a third component, responsive to the measure of the difference, outputs a first value if the coil voltage is greater than the reference voltage and a second value if the coil voltage is less than the reference voltage, which third component output is applied as input to the controller; wherein the controller executes a search algorithm that varies the one or more digital signals while observing changes in the third component output to provide a digital estimate of the coil voltage, which estimate provides a measure of the disk drive head velocity.
Patent Number: 6,894,453 Issued on 05/17/2005 to Drouin, et al.
| Inventors:
|
Drouin; David M. (Milpitas, CA);
Perahia; Avraham (San Jose, CA)
|
| Assignee:
|
Riospring, Inc. (Milpitas, CA)
|
| Appl. No.:
|
687056 |
| Filed:
|
October 16, 2003 |
| Current U.S. Class: |
318/569; 318/601; 360/75 |
| Intern'l Class: |
G11B 021/02 |
| Field of Search: |
318/459,500,569,592,594,600,601,619
360/730.1,75
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Ro; Bentsu
Attorney, Agent or Firm: Einschlag; Michael B.
Parent Case Text
This application claims the benefit of U.S. Provisional Application No. 60/420,631,
filed on Oct. 22, 2002, which is incorporated herein by reference.
Claims
1. Apparatus to provide a measure of disk drive head velocity in a disk drive
wherein movement is produced by a disk drive motion mechanism that includes a coil,
which apparatus comprises:
a controller that outputs one or more digital signals that are applied as input
to a first component, and in response, the first component outputs a reference
voltage;
a second component, responsive to voltage output across the coil and the reference
voltage, outputs a measure of a difference between the coil voltage and the reference
voltage; and
a third component, responsive to the measure of the difference, outputs a first
value if the coil voltage is greater than the reference voltage and a second value
if the coil voltage is less than the reference voltage, which third component output
is applied as input to the controller;
wherein the controller executes a search algorithm that varies the one or more
digital signals while observing changes in the third component output to provide
a digital estimate of the coil voltage, which estimate provides a measure of the
disk drive head velocity.
2. The apparatus of claim 1 wherein the first component comprises one or more resistors.
3. The apparatus of claim 2 wherein the third component is a comparator.
4. The apparatus of claim 2 wherein the second component is a differential amplifier.
5. The apparatus of claim 1 wherein the first component comprises a digital-to-analog
converter having one or more inputs, and an output from the DAC is applied as input
to a resistor.
6. The apparatus of claim 5 wherein the third component is a comparator.
7. The apparatus of claim 5 wherein the second component is a differential amplifier.
8. Apparatus that causes disk drive head velocity in a disk drive wherein movement
is driven by a disk drive motion mechanism that includes a coil to approximate
a predetermined value of disk drive head velocity, which apparatus comprises:
a current driver that applies current to the coil in response to a current signal;
a controller that outputs: (a) one or more digital signals that are applied as
input to a first component, and response, the first component outputs a reference
voltage, and (b) the current signal;
a second component, responsive to voltage output across the coil and the reference
voltage, outputs a measure of a difference between the coil voltage and the reference
voltage; and
a third component, responsive to the measure of the difference, outputs a first
value if the coil voltage is greater than the reference voltage and a second value
if the coil voltage is less than the reference voltage, which third component output
is applied as input to the controller;
wherein the controller executes a feedback algorithm that varies the current
signal while observing changes in the third component output, wherein the feedback
algorithm causes the current signal to supply more current to the coil whenever
the third component is equal to the second value and causes the current signal
to supply more current otherwise.
Description
TECHNICAL FIELD OF THE INVENTION
One or more embodiments of the present invention relate generally to method and
apparatus to measure disk drive head load/unload velocity.
BACKGROUND OF THE INVENTION
As is well known in the art, most small form factor disk drives utilize a ramp
load/unload process wherein disk drive heads are loaded onto a disk (i.e., placed
in position to read/write data from/to the disk) by causing an arm holding the
heads to rotate so that it moves down along a ramp. Further, as is also well known
in the art, when data access from/to the disk is complete, the disk drive heads
may be unloaded from the disk by causing the arm to rotate so that it moves up
along the ramp.
In order to ensure long-term disk drive reliability, the above-described ramp
load/unload process should be controlled so that no damage to the disk and disk
drive heads occurs. Generally, this involves using a servo control system that
attempts to maintain the load and unload velocity of the disk drive heads on an
optimized trajectory. As is known, this entails, among other things, measuring
disk drive head velocity during the load/unload process.
As is well known, movement of disk drive heads is caused by applying current
to
a voice coil magnet ("VCM") which causes an arm holding the disk drive heads to
rotate. Prior art methods to measure the resulting disk drive head velocity typically
entail using an analog-to-digital converter to measure a back-EMF voltage generated
in the VCM. As is well known, the VCM back-EMF is proportional to an angular velocity
of the VCM, and hence, provides a measure of disk drive head velocity. Such prior
art methods are problematic because they require circuitry that: (a) is frequently
complex, and (b) requires additional space on printed circuit boards. As a result,
such prior art methods result in increased disk drive cost.
In light of the above, there is a need to overcome one or more of the above-identified problems.
SUMMARY OF THE INVENTION
One or more embodiments of the present invention satisfy one or more of the above-identified
needs in the art. In particular, one embodiment of the present invention is an
apparatus to provide a measure of disk drive head velocity in a disk drive wherein
movement is produced by a disk drive motion mechanism that includes a coil, which
apparatus comprises: (a) a controller that outputs one or more digital signals
that are applied as input to a first component, and in response, the first component
outputs a reference voltage; (b) a second component, responsive to voltage output
across the coil and the reference voltage, outputs a measure of a difference between
the coil voltage and the reference voltage; and (c) a third component, responsive
to the measure of the difference, outputs a first value if the coil voltage is
greater than the reference voltage and a second value if the coil voltage is less
than the reference voltage, which third component output is applied as input to
the controller; wherein the controller executes a search algorithm that varies
the one or more digital signals while observing changes in the third component
output to provide a digital estimate of the coil voltage, which estimate provides
a measure of the disk drive head velocity.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows a block diagram of an apparatus that provides a measure of disk
drive head velocity, which apparatus is fabricated in accordance with one or more
embodiments of the present invention;
FIG. 2 shows a flowchart of an algorithm that is fabricated in accordance with
one or more embodiments of the present invention, which algorithm is executed by
a controller of the apparatus shown in FIG. 1 and which algorithm is used
to provide a measure of disk drive head velocity;
FIG. 3 shows a flowchart of an algorithm that is fabricated in accordance with
one or more alternative embodiments of the present invention, which algorithm is
executed by a controller in accordance with one or more alternative embodiments
of the present invention that utilize an N-bit digital-to-analog converter ("DAC")
and which algorithm is used to provide a measure of disk drive head velocity.
FIG. 4 shows a circuit diagram used to fabricate one or more embodiments of
the apparatus shown in FIG. 1;
FIG. 5 shows a flowchart of an algorithm that is fabricated in accordance with
one or more embodiments of the present invention, which algorithm causes disk drive
head velocity to approximate a predetermined value of disk drive head velocity,
i.e., a target velocity; and
FIG. 6 shows a block diagram of an apparatus that carries out the algorithm
shown in FIG. 5, which apparatus is fabricated in accordance with one or more embodiments
of the present invention.
DETAILED DESCRIPTION
One or more embodiments of the present invention measure disk drive head velocity
when it is: (a) loaded onto a disk from a ramp; or (b) unloaded from the disk onto
the ramp. As is known, the disk drive heads are affixed to an arm, and the arm
is driven by a disk drive motion mechanism, which disk drive motion mechanism includes
a coil that is often referred to as a so-called a voice coil magnet ("VCM"). In
accordance with such a configuration, the disk drive heads rotate at a fixed distance
from a pivot point. As is further known, to instigate movement of the disk drive
heads, a current pulse is applied to the VCM, which current pulse causes the arm
to start to move. After the current pulse has decayed, the arm continues to move
(due to inertia), and due to this movement, a back-EMF is generated in the VCM.
As is further well known, the VCM back-EMF is proportional to an angular velocity
of the VCM, and consequently, the linear velocity of the disk drive heads. Thus,
the VCM back-EMF provides a measure of velocity of the disk drive heads.
FIG. 1 shows a block diagram of apparatus
1000 that provides a measure
of disk drive head velocity, which apparatus
1000 is fabricated in accordance
with one or more embodiments of the present invention. Assume that apparatus
1000
utilizes a measurement bandwidth of V
D, and that V
D/2 is
the middle of that bandwidth. As shown in FIG. 1, controller
100 generates
N+1 digital signals or outputs GPIO(
0) to GPIO(N), and digital signals or
outputs GPIO(
0) to GPIO(N) are applied as input to resistors R(
0)
to R(N). In accordance with one or more embodiments of the present invention, controller
100 may be a microcontroller utilized in a disk drive, and more specifically,
controller
100 may be a digital signal processor ("DSP"). In accordance
with one or more such embodiments of the present invention, digital signals or
outputs GPIO(
0) to GPIO(N) may be provided using, for example and without
limitation, general purpose I/O outputs of a DSP. Further, assume that GPIO(
0)
to GPIO(N) and R(
0) to R(N) are chosen so that the voltage range output
from resistors R(
0) to R(N) (i.e., the range is provided by varying the
values of GPIO(
0) to GPIO(N)) varies from 0 to V
D and has a midpoint
is equal to V
D/2.
As further shown in FIG. 1, a back-EMF generated in the VCM (after a driving
current
to cause motion of the disk drive head has decayed) is applied as input to circuit
component
110 at inputs
1101 (positive input) and
1102
(negative input), where circuit component
110 has an amplification
of unity and outputs a signal V
back=V
D/2+VCM back-EMF. Circuit
component
110 may be fabricated utilizing readily available commercial components
and utilizing any one of a number of methods that are well known to those of ordinary
skill in the art.
As further shown in FIG. 1, an output from resistors R(
0) to R(N) (i.e.,
V
ref) is subtracted from the output from circuit component
110
(i.e., V
back)+V
D/2 at point
120, and the difference
is applied as input to amplifier
130 (i.e., the input to amplifier
130=V
back-V
ref+V
D/2.
As one of ordinary skill in the art can readily appreciate, amplifier
130
is used to condition signals and provide suitable voltage levels. Next, the amplified
difference output from amplifier
130 is applied as input to a positive terminal
of comparator
140 and V
D/2 is applied as input to a negative
terminal of comparator
140. Next, output
150 from comparator
140
is applied as input to controller
100. As one can readily appreciate, output
150 is 0 if V
back-V
ref+V
D/2<V
D/2,
and output
150 is, for example and without limitation, 1, if V
back-V
ref+V
D/2>V
D/2.
Amplifier
130 and comparator
140 may be fabricated utilizing readily
available commercial components and utilizing any one of a number of methods that
are well known to those of ordinary skill in the art.
In accordance with one or more embodiments of the present invention, resistors
R(
0) to R(N) have values of resistance such that the resistance of resistor
R(i)=2
i*R. As a result, by applying digital inputs having a predetermined
voltage level (0 or V) as input to resistors R(
0) to R(N), the voltage output
from resistors R(
0) to R(N) may have 2
N+1 different values. As
will be described in detail below, and in accordance with one or more embodiments
of the present invention, apparatus
1000 provides a measure of velocity
of the disk drive heads having a resolution of 2
N+1.
FIG. 2 shows a flowchart of an algorithm that is fabricated in accordance with
one or more embodiments of the present invention, which algorithm is executed by
controller
100 of apparatus
1000, and which algorithm is used to
provide a measure of disk drive head velocity. In accordance with one or more embodiments
of the present invention, the algorithm is a binary search algorithm.
As shown in FIG. 2, at box
400, controller
100 sets each of digital
outputs GPIO(
0) to GPIO(N) to 0. Control is then transferred to box
410.
At box
410, controller
100 waits for apparatus
1000 to settle
after applying outputs GPIO(
0) to GPIO(N). Control is then transferred to
box
420.
At box
420, controller
100 sets digital state variable TargetState
equal to the logical opposite of the digital state value Comparator State where
Comparator State corresponds to output
150 from comparator
140 shown
in FIG.
1. In accordance with one or more embodiments of the present invention,
(a) Comparator State has a first digital state value (for example and without limitation,
0) if VCM back-EMF<V
ref when each of digital outputs GPIO(
0)
to GPIO(N)=0; and (b) Comparator State has a second digital value (for example
and without limitation, 1) if VCM back-EMF>V
ref when each of digital
outputs GPIO(
0) to GPIO(N)=0. The algorithm then performs a binary search
to determine VCM back-EMF. Control is then transferred to
430.
At box
430, controller
100 sets N equal to the number of offset
bits used in the measurement. In accordance with one or more such embodiments of
the present invention, this determines the resolution of the velocity measurement.
Control is then transferred to a loop that starts the binary search at box
440.
At box
440, controller
100 sets GPIO(N) equal to a voltage corresponding
to logical 1, i.e., the N
th general purpose output digital signal is
set to logical 1 while the remaining digital outputs retain their previous values.
Note that the binary search starts at the most significant bit and works its way
down to the least significant bit. Control is then transferred to box
450.
At box
450, controller
100 waits for apparatus
1000 to settle.
Control is then transferred to decision box
460.
At decision box
460, controller
100 determines whether the Comparator
State (i.e., output state
150) is equal to the TargetState. In essence,
this determines whether V
ref is large enough so the difference between
VCM back-EMF signal and V
ref has changed sign. If so, control is transferred
to box
470, otherwise, control is transferred to decision box
480.
At box
470, controller
100 sets GPIO(N) equal to 0. In essence,
V
ref is too large, reduce V
ref to its value prior to being
increased at box
440. Control is then transferred to decision box
480.
At decision box
480, controller
100 determines whether N equals
0. If so, control is transferred to box
500, otherwise, control is transferred
to box
490.
At box
490, controller
100 sets N=N-1. Control is then transferred
to box
440 to continue the search.
At box
500, controller
100 converts the following: (the range of
values provided by GPIO(
0) to GPIO(N), i.e. 2
N+1)/2-the value
represented by GPIO(
0) to GPIO(N)) to a voltage, and converts this voltage
to velocity by multiplying it by a proportionality constant, which proportionality
constant may be determined by one of ordinary skilled in the art routinely without
undue experimentation based on the characteristics of particular drive mechanics
such as, for example and without limitation, strength of the magnet, number of
turns in the coil, and so forth.
One or more alternative embodiments of the present invention are fabricated by
replacing summing resistors R(
0) to R(N) of apparatus
1000 shown
in FIG. 1 with a single resistor and an N-bit DAC (digital-to-analog converter).
In accordance with one or more of such alternative embodiments: (a) N digital outputs
from controller
100 are applied as input to the N-bit DAC; (b) an output
voltage from the N-bit DAC is applied as input to the resistor, and (c) an output
voltage from the resistor (V
ref) is applied as input to point
120
of apparatus
1000 shown in FIG.
1.
FIG. 3 shows a flowchart of an algorithm that is fabricated in accordance with
one or more embodiments of the present invention, which algorithm is executed by
a controller in accordance with one or more alternative embodiments of the present
invention that utilizes an N-bit DAC and which algorithm is used to provide a measure
of disk drive head velocity. In essence, the algorithm is a binary search.
As shown in FIG. 3, at box
1400, controller
100 sets d equal to
2
(N-1), D=d, and DAC=0, where: (a) D is an output from the algorithm;
(b) DAC is an output voltage from the N-bit DAC; and (c) d represents the N-bit
digital input to N-bit DAC. Control is then transferred to box
1410.
At box
1410, controller
100 waits for apparatus
1000 to
settle
after applying an input to the N-bit DAC. Control is then transferred to box
1420.
At box
1420, controller
100 sets digital state variable TargetState
equal to the logical opposite of the digital state value Comparator State where
Comparator State corresponds to output
150 from comparator
140 shown
in FIG.
1. Like, the previous algorithm, this algorithm searches for values
of N-bit DAC that cause Comparator State to change from its initial value when
DAC was set to 0. Control is then transferred to
1430.
At box
1430, controller
100 sets N equal to the number of DAC bits.
In accordance with one or more such embodiments of the present invention, this
determines the resolution of the velocity measurement. Control is the transferred
to a loop that starts at box
1440.
At box
1440, controller
100 sets DAC=D and UP=+1. Control is then
transferred to box
1450.
At box
1450, controller
100 waits for apparatus
1000 to
settle.
Control is then transferred to decision box
1460.
At decision box
1460, controller
100 determines whether the Comparator
State (i.e., digital output state
150) is equal to the TargetState. In essence,
this determines whether a large enough amount has been subtracted from the VCM
back-EMF signal so that the difference between it and V
ref has changed
sign. If so, control is transferred to box
1470, otherwise, control is transferred
to decision box
1480.
At box
1470, controller
100 sets UP equal to -1. In essence, too
much has been subtracted from the VCM back-EMF signal, go back to reset the amount
to be subtracted, and go back to subtract a little less. Control is then transferred
to decision box
1480.
At decision box
1480, controller
100 determines whether N equals
0. If so, control is transferred to box
1500, otherwise, control is transferred
to box
1490.
At box
1490, controller
100 sets N=N-1, d=d/2, D=D+(UP*d). Control
is then transferred to box
1440.
At box
1500, controller
100 converts the following: (the range
of
values provided by the DAC)/2-the value represented by D) to a voltage, and converts
this voltage to velocity by multiplying it by a proportionality constant, which
proportionality constant may be determined by one of ordinary skilled in the art
routinely without undue experimentation based on the characteristics of particular
drive mechanics such as, for example and without limitation, strength of the magnet,
number of turns in the coil, and so forth.
FIG. 4 shows a circuit diagram used to fabricate one or more embodiments of
apparatus
1000 shown in FIG.
1. As shown in FIG. 1, digital outputs
GPIO(
0) to GPIO(N) from a controller (not shown in FIG. 4 for ease of understanding
the invention) are applied as input to resistors R(
0) to R(N), the output
from resistors R(
0) to R(N) is applied as input to summing point
120.
As further shown in FIG. 4, an input from a "positive" side of the VCM (i.e.,
VCM back-EMF VCMP) is applied as input to terminal
1101 where
it is scaled by a resistor, added to V
D/2 at summing point
121,
and applied as input to a positive terminal of differential amplifier
135.
As further shown in FIG. 4, an input from a "negative" side of the VCM (i.e., VCM
back-EMF VCMN) is applied as input to terminal
1102 where it
is scaled by a resistor, added to V
ref (to be described below), and
applied as input to a negative terminal of differential amplifier
135. As
was described above in conjunction with FIG. 1, V
ref is determined by
output from resistors R(
0) to R(N) after receiving inputs in the form of
digital outputs GPIO(
0) to GPIO(N).
As further shown in FIG. 4, the output from differential amplifier
135
is applied as input to a positive terminal of comparator
145. Finally, as
further shown in FIG. 4, V
D/2 is applied as input to a negative terminal
of comparator
140
As was described above with respect to FIG. 1, output
150 from comparator
145 is 0 if V
back-V
ref+V
D/2<V
D/2,
and output
150 is, for example and without limitation, V
D, if
V
back-V
ref+V
D/2>V
D/2. Differential
amplifier
135 and comparator
145 may be fabricated utilizing any
one of a number of suitable components that are well known to those of ordinary
skill in the art.
FIG. 5 shows a flowchart of an algorithm that is fabricated in accordance with
one or more embodiments of the present invention, which algorithm may be executed,
for example and without limitation, by controller
900 of apparatus
2000
shown in FIG.
6. This algorithm is a feedback control algorithm that utilizes
feedback of measurements of disk drive head velocity to cause the disk drive head
velocity to approximate a predetermined value of disk drive head velocity, i.e.,
a target velocity. As one can readily appreciate from FIG. 6, apparatus
2000
includes apparatus
1000 shown in FIG.
1 and adds VCM current driver
910. For this embodiment, only resistor R(
0) shown in FIG. 1 is used.
As shown in FIG. 5, at box
700, controller
900 outputs GPIO(
0)
to generate a reference voltage level corresponding to a predetermined value of
disk drive head velocity, i.e., a target velocity. Control is then transferred
to box
710.
At box
710, controller
900 waits for the circuits to settle. Control
is then transferred to box
720.
At box
720, controller
900 disables VCM current driver
910.
Control is then transferred to box
730.
At box
730, controller
900 waits for circuits to recover from disabling
of VCM current driver
910. Control is then transferred to box
740.
At box
740, controller
900 samples Comparator State (for example,
digital output state signal
950 from comparator
940 shown in FIG.
6). Control is then transferred to decision box
750.
At decision box
750, controller
900 determines whether Comparator
State=0 to determine whether the VCM back-EMF is below the reference voltage level.
If so, control is transferred to box
760, otherwise, control is transferred
to box
770.
At box
760, controller
900 sets VelocityError=+Vconstant. In essence,
the VCM back-EMF is below the reference voltage level, and more current must be
applied to the VCM to accelerate the disk drive head. Control is then transferred
to box
780.
At box
770, controller
900 sets VelocityError=-Vconstant. In essence,
the VCM back-EMF is above the reference voltage level. Control is then transferred
to box
780.
At box
780, controller
900 sets ControlOutput=(VelocityError*PROPORTIONALgain)+Integrator.
ControlOutput is an amount of current to apply to the VCM to accelerate or decelerate
the disk drive head, as the case may be, so that the velocity of the disk drive
head will approach the desired target velocity. Appropriate values of Vconstant
and PROPORTIONALgain may be determined by one of ordinary skilled in the art routinely
without undue experimentation based on the characteristics of particular drive
mechanics and performance required. Control is then transferred to box
790.
At box
790, controller
900 enables VCM current driver
910,
and sets the current output equal to ControlOutput. Control is then transferred
to box
800.
At box
800, controller
900 sums the total correction by setting,
Integrator=Integrator+(VelocityError*INTEGRATORgain). An appropriate value of INTEGRATORgain
may be determined by one of ordinary skilled in the art routinely without undue
experimentation based on the mechanical characteristics of a particular disk drive
and the performance required. Control is then transferred to box
810.
At box
810, controller
900 waits for a predetermined amount of
time
for VCM current driver
910 to output current. Control is then transferred
to decision box
820.
At decision box
820, controller
900 determines whether termination
of the algorithm has been requested. If so, control is transferred to box
830
to exit, otherwise, control is transferred to box
720.
Although various embodiments that incorporate the teachings of the present
invention have been shown and described in detail herein, those skilled in the
art can readily devise many other varied embodiments that still incorporate these teachings.
*
