Internal Profile Generation
68
Juno Step Motor Control IC User Guide
11
11.1 Juno Cycle Time
Juno ICs calculate all profile generator on a fixed, regular interval known as the cycle time. For Juno step motor ICs
the nominal cycle time value is 102.4
μ
Seconds, but this may vary by as much as +/- 1/2% over Juno’s temperature
operating range.
11.2 Profile Parameter Scaling
The profile parameters use an encoding denoted “X.Y” with X indicating the number of bits representing the integer
portion and Y indicating the number of bits used to represent the fractional component.
Specified target profile parameters are applied immediately. Whether or not these new parameters result in an
immediate change depends on the profile being drawn. For example if a new deceleration value is programmed while
the axis is accelerating this new deceleration value will not be applied until the profile enters a deceleration phase.
Example
A profile that achieves a velocity of 135,000 microsteps/sec is desired after an acceleration phase of 120 mSecs.
To convert microsteps/sec to microsteps/cycle we use: V (in microsteps/cycle) = V (in microsteps/sec) / (1.0 sec /
.000102 cycles/sec). Plugging in, we get V = 135,000 microsteps/sec / 9,765 cycles/sec = 13.825 microsteps/cycle.
To scale this command to the 16.16 format used for the Juno target velocity we multiply by 2
16
giving a 32-bit target
velocity command of 13.825 * 65,536 = 906,035.
The acceleration command must achieve the desired velocity in .120 sec * 9,765 cycles/sec = 1,172 cycles. Therefore
the acceleration is 13.825 microsteps/cycle / 1,172 cycle = .01180 microsteps/cycle
2
. To scale this command to the
8.24 format used for the Juno target acceleration we multiply by 2
24
giving a 32-bit acceleration command value to
send of .01180 * 16,777,216 = 197,971.
11.3 Profile Stop Events
Juno provides an event action mechanism that allows automatic stopping of the motor axis under various conditions
such as motion error, over temperature condition, and disable. Juno provides two types of controlled stops; a smooth
stop and an abrupt stop. In a smooth stop the motor profile decelerates at the user-specified deceleration value until
it reaches a velocity of zero. In an abrupt stop the velocity is instantaneously set to zero without a deceleration phase.
When the profile generator is active both a smooth stop and an abrupt stop will result in the user specified target
velocity register being set to zero. This means that to restart a profile the target velocity has to be reloaded. For an
abrupt stop, in addition to the target velocity being set to zero the instantaneous commanded velocity it also set to zero.
For more information on setting up and recovering from event actions refer to
Name
Format
Representation, Range & units
Velocity
16.16
signed 32 bits (-32,768 to +32,767.9998 counts/cycle/2
16
)
Acceleration
8.24
unsigned 32 bits (0 to +127.99999994 counts/cycle
2
/2
24
)
Deceleration
8.24
unsigned 32 bits (0 to +127.99999994 counts/cycle
2
/2
24
)
