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| Electrical
Features |
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The
system controller module is the brains of the LT360EX and contains
all of the analog and digital processing circuitry. Three microcontrollers
are employed: the Main System Controller, the USB Interface Controller,
and the Stepper Motor Controller. The main MCU is an ARM-7 32-bit
processor operating at 48MHz.
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Advanced Microstepping Controller
Due to the high resolution, programmble torque, controlled acceleration/
deceleration, and variable velocity operation; very demanding requirements
are placed on the motor control drive system. The EX model
utilizes a highly advanced proprietary custom microstepping controller
with unique bidirectional PWM high frequency current regulation.
This innovative design enables the control of both positive and
negative motor coil currents, all within a locked feedback control
loop. |
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The
microstepping controller must first generate precise dual sine waves
in quadrature, with the required stepping resolution of 16 microsteps.
This is handled by two very accurate16 bit DACs as shown on the left.
The true motor coil current is sensed by precision differential amplifiers.
The motor current is then compared against these waveforms and regulated
in a bidirectional PWM feedback loop to match these two DAC staircase
waveforms. |
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traces on the right show the actual motor coil currents of
7.5 Amps Peak as measured by dual Tektronix A6302 current probes.
They perfectly track both the positive and negative slopes of the
DAC waveforms. Conventional stepper drives use a fixed combination
of fast/slow decay which cannot adapt to variations in motor speed
and produce asymmetrical behavior. The bidirectional PWM drive utilized
in the EX dynamically adjusts for optimum drive at any motor
speed producing textbook perfect current waveforms, maximum square
wave drive power at high motor speed, and minimal current ripple at
zero motor speed. |
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SmartTorque
The SmartTorque feature of the LT360EX automatically reduces motor
power when the platter is not in motion. Since the worm drive is irreversible
it is not necessary to maintain full drive power to the motor merely to
hold its position. The worm drive locks the position automatically. Motor
power is reduced to half when the drive is not active. This increases motor
life and reduces unnecessary power consumption and heating both in the drive
electronics and the motor. |
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Variable Speed Operation
The EX model enables variable speed operation from 0.1RPM
to 12 RPM. The very wide 100:1 range provides the ability to handle
heavy loads at lower RPM, and lighter loads at higher RPM. As the
RPM increases the motor current decreases, thus reducing torque
as shown here in the graph. This is the common result of all electrical
motor drives. Maximum torque is produced for platter velocities
below about 3 RPM. The higher RPM range can be used for lighter
loads which may require more speed and less torque. |
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Analog Interface & Calibration
The analog control system uses both ADC and DAC components of 16 bit
resolution, as well as computer corrected linearity. Custom thin-film
resistor networks are employed to meet the temperature tracking and stability
requirements. Each LT360EX unit requires 90 minutes of automated
calibration and performance verification. |
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Universal Power Supply
The
LT360EX utilizes a high frequency power supply with power
factor correction. This provides universal world-wide voltage support,from
85-265VAC without user changes. The LT360EX is shipped with
an IEC-US power cord. If your power plug requirements are different,
you can obtain a different IEC cord as needed from your local electronics
retail stores. |
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