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Spindle Motor Drive Method for High Speed/Torque Applications using Low Voltage Supplies

IP.com Disclosure Number: IPCOM000113517D
Original Publication Date: 1994-Sep-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 180K

Publishing Venue

IBM

Related People

Erickson, KJ: AUTHOR [+2]

Abstract

A brushless DC motor drive method is described that provides a wider range of control in order to better accommodate both high startup torque requirements and high speed operation requirements in a given spindle control system. This method can be used to extend the capabilities of more conventional spindle control systems by overcoming some of the limitations placed on these systems by the motor torque constant and power supply voltage requirements. This method provides a means to obtain the starting torque needed to start a motor that has a limited torque constant, which is often required due to high operating speed provisions in order to limit the amount of back-EMF. This method also provides a means to obtain a higher operating speed with a lower power supply voltage than a conventional motor drive method.

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Spindle Motor Drive Method for High Speed/Torque Applications using
Low Voltage Supplies

      A brushless DC motor drive method is described that provides a
wider range of control in order to better accommodate both high
startup torque requirements and high speed operation requirements in
a given spindle control system.  This method can be used to extend
the capabilities of more conventional spindle control systems by
overcoming some of the limitations placed on these systems by the
motor torque constant and power supply voltage requirements.  This
method provides a means to obtain the starting torque needed to start
a motor that has a limited torque constant, which is often required
due to high operating speed provisions in order to limit the amount
of back-EMF.  This method also provides a means to obtain a higher
operating speed with a lower power supply voltage than a conventional
motor drive method.  The usual tradeoffs between the startup
requirements, operating speed requirements, and power supply
requirements still exist with this method, however this method allows
for additional degrees of freedom in motor and control system designs
as compared with conventional designs.  These degrees of freedom
allow for a more efficient motor design when used in combination with
the drive method described, and at the same time allow for a wider
range of operation which may be required to satisfy the overall
design requirements.

      Most brushless DC spindle motor control systems in use today
employ a drive method similar to that depicted in Fig. 1.  This drive
method utilizes three half-bridge drivers to drive current through
the spindle motor by turning on the Upper Drive Switch (UDS) of one
driver simultaneously with the Lower Drive Switch (LDS) of another
driver, thereby routing the drive current through two of the motor
phase windings in series.  The drive current is commutated through
the different motor phase combinations in a particular sequence in
order to rotate the spindle in a particualr sequence in order to
rotate the spindle motor in the desired direction, while the amount
of drive current is controlled by circuits that select the level at
which the drive switches are turned on.

      An alternative method to that described above can be used to
extend the startup and run speed capabilities of a conventional
spindle control system by altering the makeup of the motor and
control circuits used in the system, as depicted in Fig. 2.  This
method provides a means to drive each of the three phases of the
spindle motor independently by using full-bridge drivers instead of
half-bridge drivers, and by not connecting the motor windings
together inside the motor, but instead providing access to both sides
of each phase winding.

      This drive method can produce an equivalent drive to the motor
as produced by the system described above by properly selecting the
drive switches to turn on.  Take for example the syst...