Delta Tau GEO BRICK LV Benutzerhandbuch
Turbo PMAC User Manual
Synchronizing Turbo PMAC to External Events
347
Use for Cascaded Loops
Offset-mode following can be very useful for the implementation of cascaded servo loops. The output of
the outer loop is used as the master position for the inner position loop (and not sent directly to an
actuator). In this mode of operation, typically, the inner loop is a standard position loop; the outer loop
closes a loop on force or tool height, or some other process variable. The use of offset mode for this
purpose permits normal trajectory commands to the inner loop, with the possibility for simultaneous
corrections from the outer loop. Refer to the Cascading Servo Loops and Setting up the Servo Loop
sections for details.
the outer loop is used as the master position for the inner position loop (and not sent directly to an
actuator). In this mode of operation, typically, the inner loop is a standard position loop; the outer loop
closes a loop on force or tool height, or some other process variable. The use of offset mode for this
purpose permits normal trajectory commands to the inner loop, with the possibility for simultaneous
corrections from the outer loop. Refer to the Cascading Servo Loops and Setting up the Servo Loop
sections for details.
Changing Following Modes
The following mode is used in determining how the calculations relating motor and axis position are
performed, so changing the mode changes how these calculations would be done for subsequent moves,
creating a mismatch between motor and axis position, which could cause a jump in the motor motion on
the next move if not corrected. This is true regardless of whether or not following is enabled. To correct
for this mismatch, a PMATCH position-matching command must be executed before the next motion
program move command is processed.
Turbo PMAC automatically executes a PMATCH command any time a R (run) or S (step) command is
issued; however, if the mode is changed in the middle of a motion program, this on-line command must
be issued explicitly. A DWELL command should precede this command (to stop program lookahead);
another DWELL command should trail this (to give the command time to execute from the on-line queue).
The program sequence would look something like:
performed, so changing the mode changes how these calculations would be done for subsequent moves,
creating a mismatch between motor and axis position, which could cause a jump in the motor motion on
the next move if not corrected. This is true regardless of whether or not following is enabled. To correct
for this mismatch, a PMATCH position-matching command must be executed before the next motion
program move command is processed.
Turbo PMAC automatically executes a PMATCH command any time a R (run) or S (step) command is
issued; however, if the mode is changed in the middle of a motion program, this on-line command must
be issued explicitly. A DWELL command should precede this command (to stop program lookahead);
another DWELL command should trail this (to give the command time to execute from the on-line queue).
The program sequence would look something like:
DWELL0
; Stop lookahead
I106=3
; Change following mode
CMD"&1PMATCH"
; Re-match positions
DWELL10
; Delay for PMATCH execution
External Time-Base Control (Electronic Cams)
A more sophisticated method of coordination to external axes is that of time-base control, in which the
input signal frequency controls the rate of execution of moves and programs. Time-base control operates
on an entire coordinate system together. Specify which encoder register is receiving the input frequency,
and the relationship between the input frequency and the program rate of execution. This not only varies
the speed of moves in proportion to the input frequency (all the way down to zero frequency), but also
keeps total position synchronization. This permits operations such as multi-pass screw threading.
input signal frequency controls the rate of execution of moves and programs. Time-base control operates
on an entire coordinate system together. Specify which encoder register is receiving the input frequency,
and the relationship between the input frequency and the program rate of execution. This not only varies
the speed of moves in proportion to the input frequency (all the way down to zero frequency), but also
keeps total position synchronization. This permits operations such as multi-pass screw threading.
What Is Time-Base Control?
Turbo PMAC’s motion language expresses the position trajectories as functions of time. Whether the
moves are specified directly by time, or by speed, ultimately the trajectory is defined as a position-vs-time
function.
This is fine for a great number of applications. However, in many applications, we wish to slave the
Turbo PMAC axes to an external axis not under Turbo PMAC control (or occasionally, an independent
axis under Turbo PMAC control in a different coordinate system). In these applications, we want to
define the Turbo PMAC trajectories as functions of master position, not of time.
moves are specified directly by time, or by speed, ultimately the trajectory is defined as a position-vs-time
function.
This is fine for a great number of applications. However, in many applications, we wish to slave the
Turbo PMAC axes to an external axis not under Turbo PMAC control (or occasionally, an independent
axis under Turbo PMAC control in a different coordinate system). In these applications, we want to
define the Turbo PMAC trajectories as functions of master position, not of time.
Real-Time Input Frequency
Turbo PMAC’s method for doing this leaves the language expressing position as a function of time, but
makes time proportional to the distance covered by the master. This is done by defining a real-time input
frequency (RTIF) from the master’s position sensor, in units of counts per millisecond. For example,
define an RTIF of 32 cts/msec. Then, in time-base mode, when the program refers to a millisecond, what
it is really referring to is 32 counts of the master encoder, whatever physical distance that is. If a move is
programmed in the slave program to take two seconds, it will really take 64,000 counts of the master
encoder to complete.
makes time proportional to the distance covered by the master. This is done by defining a real-time input
frequency (RTIF) from the master’s position sensor, in units of counts per millisecond. For example,
define an RTIF of 32 cts/msec. Then, in time-base mode, when the program refers to a millisecond, what
it is really referring to is 32 counts of the master encoder, whatever physical distance that is. If a move is
programmed in the slave program to take two seconds, it will really take 64,000 counts of the master
encoder to complete.