G43.5 RTCP Type II In a previous article we discussed the SIEMENS Vector format for
5-Axis. It may come as a surprise to many that a similar function exists
within the FANUC CNC lexicon. That function is activated with the G43.5
command. G43.5 is defined by FANUC as RTCP Type II (Rotary Tool Center
Point) function. (RTCP functionality on the SIEMENS controls is called
by the command TRAORI.) While most understand that RTCP automatically
accounts for the length of the tool in 5-Axis machines with a Head/Head
rotary axis configuration, many people do not understand that it is
primarily designed to maintain the tool control point in relation to the
programmed point of the workpiece. This means that it can be and is
also used for 5-Axis machines with a Table/Table rotary axis
configurations as well as machines with Head/Table rotary axis
configurations. Maintaining this relationship between the tool control
point and the programmed point of the workpiece, results is a a program
that requires a smaller envelope within which to operate.  When viewing from the right side of a C/A 5-Axis Head, the rotary command A-90.0 causes a movement of axis A without any linear axis movements that would keep the tool in contact with the part.  If RTCP is active, the same command causes the swing of -90° with
displacements of the linear axes to maintain the tool tip at the same
location. Vector Programming Mathematically, a Tool Vector is represented by its component values
that are relative to the linear X, Y and Z axes. These component values
typically use the addresses I, J and K. The relationship of the vector
component is defined as the directional cosine. The directional cosines
of a vector are the cosines of the angles between the vector and the
three coordinate axes. A Tool Vector is always referenced with its start
point at the tip of the tool along its centerline. It is generally
terminated with its end point at the tool gauge line - the intersection
of the tool holder taper and the spindle taper.  Normally, CAM system post-processors use the tool vector data to
calculate the required rotary axis angle. However, this calculation can
become problematic for certain CAM systems and their post-processors. To deal with these problems, CNC controls are becoming more 'intelligent'. The FANUC 30i Series is one such control that has some
unique abilities when it comes to the actual NC code syntax. The FANUC
30i Series is capable of processing the tool vectors directly instead of
explicit rotary axis angles by using the G43.5 RTCP Type II command.
G43.5 provides both RTCP functionality along with the ability to use
vectors in the programming. G43.5 uses the familiar I, J & K
addressees for the vector word designations. Mathematically, all three
vector components are related. That is, the square root, of the sum of
the squares, of all three vector component values equals 1. That
relationship is defined by the following equation. SQRT (I² + J² + K²) = 1 One of the major benefits of using G43.5 RTCP Type II is that this
results in a program format that is kinematically independent. That is,
regardless of the rotary axis configuration of a given machine, the
program can run without issue. The most that one has to do, generally
speaking, is modify tool change sequences depending upon the
commissioning of any given machine tool. A great article on the benefits
of kinematic independence through the use of Vector Programming can be
found at the link below. Now, let's take a look at how it is actually implemented for a
machine with a C/A 5-Axis Head configuration with the following sample
file 5-AXIS_PRISMATIC.NC . This sample file will machine five faces of a part 20.0" x 10.0" x 5.0".
In block number N13 of the program, we see the machine positions to
X-14.5 Y4.25. In block number N14, RTCP Type II is activated with the
appropriate tool length offset and a tool vector of I0.0 J0.0 K1.0 .
This tool vector is equivalent to a rotary axis position of A0.0 C0.0  The facing operation continues to completion at X12.0 Y-4.75 and then retracts to Z4.0 .  Now this is where things get interesting. In block number N32, the tool
now gets a plane change with G18 and a vector change to I0.0 J1.0 K0.0.
This orientation is equivalent to A-90.0 C0.0 . However, the tool tip
location has NOT changed because we have RTCP Type II active.  In block number N33, we have the FANUC AICC High Speed settings for the
facing operation on the back face of our part. Block number N34 is the
initial XY positioning for the facing operation. Block number N35 is the
final positioning move before beginning the feed to Y5.0 and machining
the back face of the part.  The video below shows the complete tool motion of the program using FANUC RTCP Type II.
Those who may have an interest can download the program used in the video above. 5-AXIS_PRISMATIC.NC A program with more detailed use of G43.5 RTCP Type II is also available. NAS_979_5X.NC
With G43.5 RTCP Type II, the standard data resolution of 3 decimal
places for Millimeter and 4 decimals places for Inch is insufficient.
The least increment system should be changed from the default IS-B to
IS-E. This will allow a resolution of 7 decimal places. By doing this,
your vectors will have the greatest precision possible and reduce the
rounding error to two decimal places LESS than the standard unit
precision (IS-B) on a FANUC for either Inch or Millimeter. This can be
accomplished by modifying Parameters #1013 and #5042. The higher decimal resolution for coordinates and vectors in a
program insures the most accurate and smooth High Speed motion while
using G43.5 RTCP Type II. Additionally, while we are using vectors in
our NC program, the CNC Control is still calculating the rotary axis
angles, monitoring and displaying them during operation. By allowing the
CNC control to make its calculations using the most accurate vector
data will result in a more accurate calculation of an angular addresses
values and more accurate positioning. To sum up, the FANUC G43.5 RTCP Type II command is an advanced tool
that provides a great deal of programming flexibility in addition to
solving problems with machine kinematics encountered by CAM systems. It
is worth considering configuring your CAM Post-Processor to use FANUC
G43.5 RTCP Type II Vector Programming to take advantage of the benefits
provided. |
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FANUC G43.5 RTCP Type II - Vector Programming for 5-Axis
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