Delta Tau GEO BRICK LV User Manual
Turbo PMAC User Manual
Motor Compensation Tables and Constants
163
Terms whose names consist of two letters, with the second letter an S, multiply the results of an entire
block. These terms are treated as integers with a range of +/-8,388,608.
block. These terms are treated as integers with a range of +/-8,388,608.
The PID terms Ixx30 – Ixx39, Ixx63 – Ixx65, and Ixx67 are not used. Ixx68 is used as the “friction
feedforward” term for the ESA, just as it is for the PID. Ixx69 is used for the ESA, but in a slightly
different manner from the PID. In the PID, Ixx69 is a truncation limit on the control effort output that
does not affect smaller command values; in the ESA it is an output scale factor that affects all output
command values.
feedforward” term for the ESA, just as it is for the PID. Ixx69 is used for the ESA, but in a slightly
different manner from the PID. In the PID, Ixx69 is a truncation limit on the control effort output that
does not affect smaller command values; in the ESA it is an output scale factor that affects all output
command values.
Cascading Servo Loops
The open structure of Turbo PMAC’s servo loops and the ability to specify which registers are used for
its inputs and outputs provide the user with powerful capabilities such as the ability to “cascade” servo
loops. In this technique, the output of one servo loop (one Turbo PMAC “motor”) is used as an input to
another servo loop, bringing the capabilities of both loops to bear on a single actuator. The outer loop
does not drive an actuator directly; instead, it dynamically modifies the set point of the inner loop in an
effort to drive its own error to zero.
its inputs and outputs provide the user with powerful capabilities such as the ability to “cascade” servo
loops. In this technique, the output of one servo loop (one Turbo PMAC “motor”) is used as an input to
another servo loop, bringing the capabilities of both loops to bear on a single actuator. The outer loop
does not drive an actuator directly; instead, it dynamically modifies the set point of the inner loop in an
effort to drive its own error to zero.
This technique has many possible uses. The most common is to be able to close an auxiliary loop around
a standard position loop. The auxiliary loop controls some quantity affected by the position loop’s
motion, such as torque or force applied, or distance from a surface. The coupling of the loops can be
turned on and off, permitting easy switching between control modes.
Common uses of this technique include:
a standard position loop. The auxiliary loop controls some quantity affected by the position loop’s
motion, such as torque or force applied, or distance from a surface. The coupling of the loops can be
turned on and off, permitting easy switching between control modes.
Common uses of this technique include:
•
Web tensioning
•
Torque-limited screwdriving
•
Metal bending
•
Controlled-force part insertion
•
Height control over uneven surface (e.g. for auto-focus)
The inner loop in these applications is typically a standard position loop driving a real actuator with a
standard position feedback device such as an encoder or resolver. The first step in setting up such an
application is to get this loop working in standard positioning mode (running at continuous velocity if
appropriate).
standard position feedback device such as an encoder or resolver. The first step in setting up such an
application is to get this loop working in standard positioning mode (running at continuous velocity if
appropriate).
The outer loop in these applications uses a feedback sensor measuring whatever quantity the outer loop is
to be controlled. Often these force or torque transducers such as strain gages or tensioning dancer arms,
or distance (gap) transducers employing capacitive or ultrasonic mechanisms.
to be controlled. Often these force or torque transducers such as strain gages or tensioning dancer arms,
or distance (gap) transducers employing capacitive or ultrasonic mechanisms.
By engaging and disengaging the outer loop, the user can switch between standard position control using
just the inner loop, as when not meeting the resistance of a surface, and control of the auxiliary function,
as when pushing with controlled force against a surface. The transition is simple to perform, and smooth
in operation.
just the inner loop, as when not meeting the resistance of a surface, and control of the auxiliary function,
as when pushing with controlled force against a surface. The transition is simple to perform, and smooth
in operation.
A second use of this technique is to build a more complex filter than you can with the standard filter for a
single motor (e.g. incorporating a double notch filter). By using the output of the first filter as the input to
the second, you can chain them together and get the action of both filters between the command and the
output. While the general principle is the same, the details of the setup and the process for getting this
going will differ. The sections immediately following cover the process for setting up hybrid control. A
special section further down describes the differences in setting up using two loops to control a single
quantity.
single motor (e.g. incorporating a double notch filter). By using the output of the first filter as the input to
the second, you can chain them together and get the action of both filters between the command and the
output. While the general principle is the same, the details of the setup and the process for getting this
going will differ. The sections immediately following cover the process for setting up hybrid control. A
special section further down describes the differences in setting up using two loops to control a single
quantity.