Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2001-06-08
2004-09-21
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06795265
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally related to the field of mass media information storage devices, and more particularly to a drive circuit and method for using a piezo actuator in both a charge mode and a voltage mode.
BACKGROUND OF THE INVENTION
Hard disk drives are mass storage devices that include a magnetic storage media, e.g. rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servo circuit, and control circuitry to control the operation of hard disk drive and to properly interface the hard disk drive to a host system or bus.
FIG. 1
shows an example of a prior art disk drive mass storage system
10
. Disk drive system
10
interfaces with and exchanges data with a host
32
during read and write operations. Disk drive system
10
includes a number of rotating platters
12
mounted on a base
14
. The platters
12
are used to store data that is represented as magnetic transitions on the magnetic platters, with each platter
12
coupleable to a head
16
which transfers data to and from a preamplifier
26
. The preamp
26
is coupled to a synchronously sampled data (SSD) channel
28
comprising a read channel and a write channel, and a control circuit
30
. SSD channel
28
and control circuit
30
are used to process data being read from and written to platters
12
, and to control the various operations of disk drive mass storage system
10
. Host
32
exchanges digital data with control circuit
30
.
Data is stored and retrieved from each side of the magnetic platters
12
by heads
16
which comprise a read head
18
and a write head
20
at the tip thereof. The conventional readhead
18
and writehead
20
comprise magneto-resistive heads adapted to read or write data from/to platters
12
when current is passed through them. Heads
16
are coupled to preamplifier
26
that serves as an interface between read/write heads
18
/
20
of disk/head assembly
10
and SSD channel
28
. The preamp
26
provides amplification to the waveform data signals as needed. A preamp
26
may comprise a single chip containing a reader amplifier
27
, a writer amplifier, fault detection circuitry, and a serial port, for example. Alternatively, the preamp
26
may comprise separate components rather than residing on a single chip.
Piezo actuators have improved performance when driven by quantities of charge versus the amount of voltage applied to it. The charge mode drive improves two important areas of performance, both well documented in the literature, namely, effects over temperature, and effects due to hysteresis. To operate a piezo actuator in a charge mode configuration, the drive circuit output must be placed in a high impedance, open loop state. Disadvantageously, once in an high impedance state, the piezo actuator can drift through charge loss, wander due to transducer effects, or simply wander due to a variety of effects and lack of feedback.
There is desired an improved piezo actuator drive circuit that can be advantageously operated in a charge mode configuration without the conventional drawbacks discussed above. Moreover, there is desired a piezo actuator drive allowing for a varying number of piezo elements, such as up to 8 elements.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a piezo actuator driver having a low frequency compensation loop formed from the piezo actuator output to the driver input. The driver circuit is adapted to drive multiple piezo actuators, which number may vary from drive to drive. This circuit advantageously results in a closed loop system having a charge mode operation within a bandpass that can be tuned for desired operation. Below the bandpass turn on the circuit operates in the voltage mode, and the closed loop system restores the piezo output to a defined DC voltage and compensates for any wandering effects. The closed loop system also compensates for any DC current mismatches in the closed loop configuration such that the piezo output is centered around a desired DC operating point.
The present invention advantageously uses a second amplifier with a resistor/capacitor configured as an integrator to set up the DC restore for the piezo driver and produce a highpass response. At high frequencies above the cut on of the loop, the driver is advantageously in a charge mode drive. However, below the cut on frequency, the driver is in a voltage mode and restoring the output to a commanded DC voltage. This circuit is compatible with a voltage mode drive, yet provides a charged mode solution without the conventional drawbacks including wandering output DC voltage. Offsets are compensated by the loop.
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Hutsell Larry G.
Malang Keith W.
Martin Doug
Murphy Terence J.
Brady W. James
Hudspeth David
Swayze, Jr. W. Daniel
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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