Delta Tau GEO BRICK LV User Manual
Turbo PMAC User Manual
292
Writing and Executing Motion Programs
PVT-Mode Moves
For the user who desires more direct control over the trajectory profile, Turbo PMAC offers Position-
Velocity-Time (PVT) mode moves. In these moves, you specify the axis states directly at the transitions
between moves (unlike in blended moves). This requires more calculation by the host, but allows tighter
control of the profile shape. For each piece of a move, you specify the end position or distance, the end
velocity, and the piece time.
Velocity-Time (PVT) mode moves. In these moves, you specify the axis states directly at the transitions
between moves (unlike in blended moves). This requires more calculation by the host, but allows tighter
control of the profile shape. For each piece of a move, you specify the end position or distance, the end
velocity, and the piece time.
Mode Statement
Turbo PMAC is put in this mode with the program statement PVT{data}, where {data} is a floating-
point constant, variable, or expression, representing the piece time in milliseconds. If I42 is set to the
default value of 0, Turbo PMAC converts this value to a 24-bit value with 12 bits of integer and 12 bits of
fraction. This provides a range of up to 4096 milliseconds (just over 4 seconds) with a resolution of about
¼-microsecond. If I42 is set to 1, Turbo PMAC converts this to a 12-bit integer value with no fractional
component (rounding to the nearest integer). This mode is mainly for compatibility with older non-Turbo
PMAC applications.
point constant, variable, or expression, representing the piece time in milliseconds. If I42 is set to the
default value of 0, Turbo PMAC converts this value to a 24-bit value with 12 bits of integer and 12 bits of
fraction. This provides a range of up to 4096 milliseconds (just over 4 seconds) with a resolution of about
¼-microsecond. If I42 is set to 1, Turbo PMAC converts this to a 12-bit integer value with no fractional
component (rounding to the nearest integer). This mode is mainly for compatibility with older non-Turbo
PMAC applications.
The move time may be changed between moves, either with another PVT{data} statement, or with a
TM{data} statement if I42 = 0, or a TA{data} statement if I42 = 1. The program is taken out of this
mode with another move mode statement (e.g. LINEAR, RAPID, CIRCLE, SPLINE).
TM{data} statement if I42 = 0, or a TA{data} statement if I42 = 1. The program is taken out of this
mode with another move mode statement (e.g. LINEAR, RAPID, CIRCLE, SPLINE).
Move Statements
A PVT mode move is specified for each axis to be moved with a statement of the form
{axis}{data}:{data}, where {axis} is a letter specifying the axis, the first {data} is a value
specifying the end position or the piece distance (depending on whether the axis is in absolute or
incremental mode), and the second {data} is a value representing the ending velocity.
The units for position or distance are the user length or angle units for the axis, as set in the Axis
Definition statement. The units for velocity are defined as length units divided by time units, where the
length units are the same as those for position or distance, and the time units are defined by variable Isx90
for the coordinate system (feedrate time units). The velocity specified for an axis is a signed quantity.
{axis}{data}:{data}, where {axis} is a letter specifying the axis, the first {data} is a value
specifying the end position or the piece distance (depending on whether the axis is in absolute or
incremental mode), and the second {data} is a value representing the ending velocity.
The units for position or distance are the user length or angle units for the axis, as set in the Axis
Definition statement. The units for velocity are defined as length units divided by time units, where the
length units are the same as those for position or distance, and the time units are defined by variable Isx90
for the coordinate system (feedrate time units). The velocity specified for an axis is a signed quantity.
Turbo PMAC Calculations
From the specified parameters for the move piece, and the beginning position and velocity (from the end
of the previous piece), Turbo PMAC computes the only third-order position trajectory path to meet the
constraints. This results in linearly changing acceleration, a parabolic velocity profile, and a cubic
position profile for the piece.
of the previous piece), Turbo PMAC computes the only third-order position trajectory path to meet the
constraints. This results in linearly changing acceleration, a parabolic velocity profile, and a cubic
position profile for the piece.
Problems in Stepping
Since you can specify (directly or indirectly) a non-zero end velocity for the move, it is not a good idea to
step through a program of transition-point moves, and great care must be exercised in downloading these
moves in real time. With the use of the BLOCKSTART and BLOCKSTOP statements surrounding a series
of PVT moves, the last of which has a zero end velocity, it is possible to use a Step command to execute
only part of a program.
step through a program of transition-point moves, and great care must be exercised in downloading these
moves in real time. With the use of the BLOCKSTART and BLOCKSTOP statements surrounding a series
of PVT moves, the last of which has a zero end velocity, it is possible to use a Step command to execute
only part of a program.
Use of PVT to Create Arbitrary Profiles
The PVT mode is the most useful for creating arbitrary trajectory profiles. It provides a "building block"
approach to putting together parabolic velocity segments to create whatever overall profile is desired.
The diagram PVT Segment Shapes, below, shows common velocity segment profiles. PVT mode can
create any profile that any other move mode can.
approach to putting together parabolic velocity segments to create whatever overall profile is desired.
The diagram PVT Segment Shapes, below, shows common velocity segment profiles. PVT mode can
create any profile that any other move mode can.