Texas Instruments Stellaris, Руководство пользователя

Страница: 20 / 45

User Interfaces
20 November 4, 2009
1
(cont.)
Fixed Rise Time This value is used when Open-loop PWM control mode is chosen.
This value controls the amount of time that the winding is left turned
on at the beginning of a step, before PWM is used to control the
current in the winding. This allows the current in the winding to rapidly
rise at the beginning of the step. This value is specified in
microseconds. It should be adjusted with care because if the amount
of time is too long, then the current in the winding may exceed the
rating for the motor.
PWM Frequency This is the frequency used for PWM, when Open-loop or Closed-loop
PWM control mode is chosen.
Chopper Off
Blanking Time This value is used to control how long the chopper leaves the voltage
off, after it turns off the winding when the drive current threshold is
reached. At the end of the blanking time, the winding is turned on
again and the chopper resumes measuring the winding current.
Motor Parameters
2
Decay Mode
Slow In Slow Decay mode, during the time that no voltage is applied to the
winding, the low-side switches on the H-bridge are closed. This allows
current to continue to circulate in the winding and decay slowly.
Fast In Fast Decay mode, during the time that no voltage is applied to the
winding, all the switches are open. The current can no longer circulate
and decays quickly.
3
Step Mode
Full With full stepping, voltage is always applied to both windings, and a
four-step stepping sequence is used.
Half With half stepping, the voltage is off during part of the stepping
sequence, and an eight half-step stepping sequence is used.
Micro With micro stepping, the whole step is divided into 8 micro-steps. The
current applied to the windings is varied sinusoidally, piecewise at
each micro-step time.
Wave Wave stepping is the same as full stepping, except that voltage is
applied to only one winding at a time.
4 Holding Current This is the amount of current that should be applied to the windings
when the motor is stopped. This increases the holding torque of the
motor. Typically this value should be 0, or a fraction of the drive
current.
5 Winding
Resistance This is the winding resistance of the motor that is used. This value
should be entered by the user if the motor type is changed. This value
is used in order to calculate the correct PWM duty cycle if PWM
control mode is used.
6 Maximum Current Sets a fault current level. If the current rises above this level, the
hardware triggers a fault and places the motor in a safe configuration.
Table 2-2. Description of Configuration Controls (Continued)
Item No. Name Description