The LINTOL Command `[ML]`

Linear motions on a NC machine are linear with respect to the machine control point. When a move includes a change in one or more of the rotary axes, the tool tip path with respect to the part will not be linear. The amount of deviation from the straight line is a function of the rotation amount and the distance between the rotary axis and the tool tip. Deviations grow larger as the rotation amount or the distance from rotary axes increases.

The problem can be eliminated by insuring that no single motion ever requires a large rotary move. Setting INTOL and OUTTOL parameters in the CAM system to a small value will generate more intermediate points, which will help eliminate the linear tolerance problems. A more effective and optimal solution is to use the LINTOL command, which specifies an acceptable deviation of the straight line motion of the tool tip from the desired CL data linear path. When LINTOL is active, GENER will choose the rotary solution (or pose) that keeps tool axis deviations to a minimum.

Some modern controllers have a built in linearization capability, which eliminates the requirement to linearize in the post-processor. See “Rotating Tool Center Point” for more information.

The LINTOL command is valid for machines having one or more continuous rotary axes. The following functions are available:

“Linearization Activation”

“Linearization Tool-Tip Tolerance”

“Linearization Tool Length Adjustment”

“Linearization Angular Tolerance”

“Linearization Stepping Control”

“Singularity Push-Thru”

“Tool-Tip-Only Linearization”

“Linearization with RTCP”

“Linearization Spline Fitting”

“Rotary Turn-Around”

“Linearization Path Planning”

“Forced Path-Planning Scan”

“Singular Pre-Positioning”

“Rotary Winding”

Linearization Activation

$\textbf{LINTOL /} \begin{pmatrix}\begin{array}{l} \textbf{ON} \\ \textbf{OFF} \end{array}\end{pmatrix}$

OFF disables linearization. ON re-enables linearization using the last specified settings. Generally post-processors will enable linearization by default.

$\textbf{LINTOL / OFF},\textbf{NEXT}$

The NEXT option with OFF disables linearization for the next motion only, whether feed or rapid. Use this feature to enable a change in rotary axis pose on a feed positioning motion, or on a rapid motion when rapid linearization is active.

Linearization Tool-Tip Tolerance

The following two commands are equivalent:

$\textbf{LINTOL / } \mathit{feed} \; \big[,\mathit{rapid}\,\big]$

$\textbf{LINTOL / } {\small \sim}\!\begin{pmatrix} \begin{array}{l} \textbf{FINE}, \mathit{feed} \\ \textbf{COARSE}, \mathit{rapid} \end{array}\,\end{pmatrix}$

The feed value specifies the allowable tool tip deviation from the programmed straight-line path permitted during motions at feed. The rapid value similarly specifies the allowable tool tip deviation during rapid moves. By default, linearization of rapid motions will not occur if a rapid value is omitted.

Whenever necessary, GENER automatically generates intermediate points along the tool path to insure that any deviation caused by rotary axis swing does not exceed the specified tolerance. If the specified tolerance cannot be achieved, GENER will diagnose this condition and use the best possible tolerance.

The choice of rotary axis position is limited while linearization is active. On a 5 axis machine there are generally two possible rotary solutions (or poses) that satisfy any given tool axis orientation. GENER will always choose the orientation that results in the least amount of tool axis deviation during the move. This is known as “large circle interpolation”. Note that GENER may choose a solution that is outside travel limits, instead of one that is inside travel limits, in order to satisfy the rotary axis pose requirements imposed by large circle interpolation. Path planning and rotary-turn-around features (both described below) can eliminate or reduce this problem.

LINTOL is not active during rapid motions if a rapid tolerance value is not specified. This means that rapid motions will be output without regard to the actual motion of the tool tip with respect to the part and without regard to the change of the tool axis from start to end of the motion. Only the final position is important with a non-linearized rapid motion. On the other hand, if rapid linearization is active, GENER will segment rapid motions in order to respect the specified straight line tolerance at the tool tip and by default will choose a rotary pose that minimizes tool axis deviations during the move (in exactly the same way that feed linearization is handled). This restriction on choice of rotary pose may inhibit the use of path planning, preferred positioning and overtravel avoidance features. See “Tool-Tip-Only Linearization” for details.

Linearization Tool Length Adjustment

GENER computes linearization intermediate points based on the distance between the rotary axis pivot point and the tool tip. The LENGTH option can be used to adjust the pivot point to tool tip distance, without affecting the output coordinates, by defining the expected gauge length of the tool.

$\textbf{LINTOL / LENGTH}, \begin{pmatrix}\,\begin{array}{l} \mathit{length} \\ \textbf{ON} \\ \textbf{OFF} \end{array}\,\end{pmatrix}$

The length value should specify the longest expected gauge length that will be used at the machine, measured in CL input units (e.g., inches for UNITS/INCHES; millimeters for UNITS/MM). OFF (the default) disables any gauge length adjustment. ON re-enables the last specified gauge length value.

Linearization Angular Tolerance

When LINTOL is active, GENER forces the tool axis to follow the path of least change while interpolating from one point to the next. This generally produces a smooth change in tool orientation when combined with the segmentation that occurs due to tool tip linearization. However, it is possible to specify an additional angular tolerance, to have GENER measure and limit the amount of angular wobble permitted in linearized feed motions.

$\textbf{LINTOL / ANGLE}, \begin{pmatrix}\,\begin{array}{l} \mathit{degrees} \\ \textbf{DIST},\mathit{tolerance} \\ \textbf{FINE} \\ \textbf{ON} \\ \textbf{OFF} \end{array}\,\end{pmatrix}$

FINE tolerance keeps wobble within two pulse widths of the rotary axes (e.g., 0.002 degrees on a rotary with a 0.001 resolution). Degrees limits wobble of the tool axis to the specified value. A tolerance can be specified to limit wobble measured at both the top of the tool (defined by the tool length) and at the cutting edge (defined by the tool diameter). If the specified tolerance cannot be achieved, GENER will diagnose this condition and use the best possible tolerance.

OFF disables angular tolerance (this is the default), which means that GENER will only measure and control tool-path tolerance at the tool tip.

Angular tolerance applies to feed linearization motions only.

Linearization Stepping Control

The following command affects how intermediate points are calculated along the motion being linearized.

$\textbf{LINTOL / SMOOTH}, \begin{pmatrix}\,\begin{array}{l} \textbf{ON} \\ \textbf{OFF} \end{array}\,\end{pmatrix}$

In V20 and earlier releases of GENER, the linearized intermediate step distances would tend to decrease as the motion was subdivided, resulting in potentially very small subdivisions at the end of very large rotary moves. Starting with V21, the linearization logic was enhanced to eliminate the bias that was causing step sizes to progressively decrease, which results in smoother stepping. OFF (the default) selects the old behavior. ON selects enhanced stepping.

Singularity Push-Thru

When the tool axis vector is parallel to the axis of rotation of one of the rotary axes, that rotary axis is said to be “singular”. This is because the orientation has no real effect on the tool-to-part relationship. The machine rotary axis behavior as it approaches singularity can be seemingly quite erratic. Quite often a very large change in machine rotary axis position is necessary to reflect a very small change in tool axis vector orientation with respect to the part.

$\textbf{LINTOL / THRU}, \begin{pmatrix}\,\begin{array}{l} \mathit{angle} \\ \textbf{ON} \\ \textbf{OFF} \end{array}\,\end{pmatrix}$

The THRU option activates special singularity processing that will attempt to minimize the rotation of the singular axis as the tool axes traverses through or close to singularity. Without this option, the rotation of the singular axes can be as much as 180 degrees within a very short span of motion in part space, which is necessary to maintain an exact tool-to-part orientation at all times. Although this is mathematically the “correct” solution, the resulting dwell mark might be unacceptable. The THRU option replaces this large singular rotation by a very short rotation of the second non-singular rotary axis, thereby eliminating the dwell mark. Note that the choice of angle is important, since this can result in a tool axis deviation in part space by as much as 2*angle. The angle is restricted to the range 0.2 through 3 degrees.

THRU,OFF disables push-thru processing; THRU,ON enables push-thru processing at the last specified angle (1 degree by default).

Push-thru processing should only be enabled when it is more acceptable to have a tool axis deviation of the specified angle than it is to have a dwell caused by a near 180 degree rotation of one of the machine’s axes.

Tool-Tip-Only Linearization

Tool-tip-only linearization is a feature that generates straight line motion at the tool tip, while allowing the rotary axes to position independently to a final position. GENER does not impose any limitations on the rotary axis pose when tool-tip-only linearization is active.

$\textbf{LINTOL / TLANGL}, \begin{pmatrix}\,\begin{array}{l} \textbf{ON} \\ \textbf{OFF}\,\big[,\textbf{ALL}\,\big] \end{array}\,\end{pmatrix}$

ON (the default) specifies standard tool angle linearization control, which limits GENER to selecting the single rotary pose that satisfies the requirements imposed by large circle interpolation.

OFF disables large circle interpolation for RAPID linearized motions only. This option has no effect unless rapid linearization is active. By disabling large circle interpolation for rapid motions, GENER is then free to choose any rotary pose on a positioning motion to satisfy path planning, preferred positioning and overtravel avoidance features. Note that although the tool tip will move in a straight line with respect to the part, the axis of the tool is not constrained in any way.

OFF,ALL disables large circle interpolation for all linearized motions; both rapid and feed. Tool-tip-only linearization on feed motions should only be used on feed positioning motions and never when the tool is in contact with the final part.

Linearization with RTCP

As mentioned at the start of this section, some modern controllers have a built in linearization capability, which should eliminate the requirement to linearize in the post-processor. See “Rotating Tool Center Point” for more information. However, some controllers, while providing tool tip linearization, do not support “large circle interpolation” to ensure the minimum amount of tool axis deviation during the move. GENER provides the following LINTOL option to overcome this limitation:

$\textbf{LINTOL / RTCP}, \begin{pmatrix}\,\begin{array}{l} \textbf{ON}\,\big[,\textbf{FINE}\,\big] \\ \textbf{OFF} \end{array}\,\end{pmatrix}$

ON enables the output of intermediate linearization generated points while RTCP is active. Use this option if gouging occurs on motions with a large change in rotary position while RTCP is active. Use “ON,FINE” to limit linearization of RTCP motions to cutting motions only; RAPID and high feed motions will not be linearized. OFF (the default) inhibits the output of linearized intermediate points while RTCP is active.

Linearization Spline Fitting

Linearization of motions with a large change in rotary axis position, or when the tool tip is far from the rotary pivot, may generate many intermediate motions. This can greatly increase total program size. GENER provides a LINTOL spline fitting option that may reduce the total tape length on machines that support 5D spline interpolation.

$\textbf{LINTOL / SPLINE}, \begin{pmatrix}\,\begin{array}{l} n \\ \textbf{ON} \\ \textbf{OFF} \end{array}\,\end{pmatrix}$

The value n defines the minimum number of linearized intermediate points that must be output for a single motion in order to be a candidate for spline fitting. A minimum of 4 points is required for spline fitting. GENER will attempt to interpolate the motion using 5D spline interpolation (if available). OFF (the default) disables linearization spline fitting. ON re-enables linearization spline fitting.

Rotary Turn-Around

Rotary turn-around (RTA) provides for automatic retraction and repositioning during LINTOL to avoid travel limitations. RTA is only available for 5-axis machining (i.e., 2 rotary axes). It is activated when the current tool path is about to exceed travel limits and the alternate solution tool path is within travel limits. RTA is controlled by the following command:

$\textbf{LINTOL / ROTREF}, \begin{pmatrix}\,\begin{array}{l} \textbf{ON} \\ \textbf{OFF} \end{array}\,\end{pmatrix}$

OFF disables RTA. ON re-enables RTA using the last specified settings. Some post-processors will enable RTA by default. RTA settings may be defined in the post-processor by default, but can also be specified using the following command:

$\textbf{LINTOL / ROTREF } {\small \sim}\!\begin{bmatrix} , \begin{array}{l} \begin{pmatrix}\begin{array}{l} \textbf{BACK} \\ \textbf{FEDTO} \end{array}\end{pmatrix} ,\mathit{dist} \begin{bmatrix} , \begin{pmatrix}\begin{array}{l} \textbf{IPM} \\ \textbf{MMPM} \\ \textbf{IPR} \\ \textbf{MMPR} \\ \textbf{PERMIN} \\ \textbf{PERREV} \end{array}\end{pmatrix} ,\mathit{feed}\, \end{bmatrix} \\ \begin{pmatrix}\begin{array}{l} \textbf{RTRCTO} \\ \textbf{RAPTO} \end{array}\end{pmatrix} ,\mathit{dist} \end{array} \end{bmatrix} \; \ldots$

$\hspace{3.52cm} \ldots \; \begin{bmatrix} , \begin{pmatrix}\,\begin{array}{l} \textbf{XAXIS} \\ \textbf{YAXIS} \\ \textbf{ZAXIS} \end{array}\,\end{pmatrix} , \begin{pmatrix}\,\begin{array}{l} \mathit{coord} \\ \textbf{NOMORE} \end{array}\,\end{pmatrix} \end{bmatrix} \begin{bmatrix} ,\textbf{LENGTH}, \begin{pmatrix}\begin{array}{l} \textbf{ON} \\ \textbf{OFF} \end{array}\end{pmatrix}\end{bmatrix} \; \ldots$

$\hspace{3.52cm} \ldots \; \begin{bmatrix} ,\textbf{AXIAL}, \begin{pmatrix}\begin{array}{l} \textbf{ON} \\ \textbf{OFF} \end{array}\end{pmatrix}\end{bmatrix} \; \ldots$

$\hspace{3.52cm} \ldots \; \begin{bmatrix} ,\textbf{OFSETL}, \begin{pmatrix}\begin{array}{l} dx,dy \big[,dz \,\big] \\ \textbf{ON} \end{array}\,\end{pmatrix} \end{bmatrix} \, \begin{bmatrix} , \begin{pmatrix}\begin{array}{l} \textbf{LEFT} \\ \textbf{RIGHT} \end{array}\,\end{pmatrix} , \begin{pmatrix}\begin{array}{l} \mathit{dist} \\ \textbf{ON} \end{array}\,\end{pmatrix} \end{bmatrix}$

BACK specifies a retraction distance along the tool axis at the current or specified feed. RTRCTO specifies an additional retraction at rapid, also along the tool axis. RAPTO specifies a plunge motion along the new tool axis at rapid. FEDTO specifies an additional plunge motion at the current or specified feed. One or more of these keywords can be omitted to reduce the number of steps during RTA. For example, BACK can be omitted to eliminate the feed retract.

A clearance plane can also be specified in machine coordinates using one of the XAXIS, YAXIS or ZAXIS keywords and the machine coordinate value. RTA will position to the clearance plane after the BACK and RTRCTO moves, staying on this plane while positioning above the first RAPTO or FEDTO point. The LENGTH,OFF option can be used to automatically remove and reinstate tool length compensation on the motions to and from the clearance plane. By default length compensation is not changed during RTA (i.e., LENGTH,ON). The clearance plane and LENGTH options are modal (specify NOMORE with one of XYZAXIS to disable the extra clearance motion).

The AXIAL,ON option can be used to align the tool parallel to the rotary axis being repositioned, after retracting the tool and before the rotary repositioning motion is output. This avoids sweeping the tool in a large arc through the workpiece space, which can allow the RTA action to be performed much closer to the workpiece (i.e., with smaller clearances). By default the tool axis is not straightened during RTA repositioning (i.e., AXIAL,OFF), The AXIAL option is modal.

When a T-slot tool or a non-symmetrical tool (e.g., an ultrasonic tool) is loaded, the tool must first be moved away from the stock wall to a clearance position before the classic RTA sequence can be generated by moving the tool along the tool axis. The RTA's OFSETL, LEFT and RIGHT parameters define an extra offset that moves the tool out of the slot or away from the wall. The offset can be specified either as an OFSETL vector, which defines the direction and amount of the offset, or as a scalar, where a LEFT or RIGHT keyword indicates the direction of the offset.

The OFSETL dx,dy,dz parameters define a vectorial offset. The direction is expressed in the local coordinate frame defined by the motion direction. The axes of this local coordinate system (CS) are: the x-axis, defined by the motion direction; the z-axis, defined by the tool axis direction; and the y-axis, defined as the cross product of z × x.

The offset direction can also be specified using either the LEFT or RIGHT keywords, where the amount of the offset is given by a scalar dist value. When CUTCOM diameter compensation is active and its (LEFT|RIGHT) specification does not match the RTA (LEFT|RIGHT) specification, then the CUTCOM specification takes precedence (the OFSETL vector is not affected by CUTCOM).

An offset value of 0.0 or an offset vector of zero length disables the feature. The last active offset can be reactivated by specifying (OFSETL|LEFT|RIGHT),ON. The last active offset type and direction are reactivated regardless of the OFSETL, LEFT or RIGHT keyword used.

The orientation shift from one rotary solution to the next occurs on the lateral positioning move between the last retract motion and the first plunge motion.

Linearization Path Planning

Linearization path planning (LPP) can:

Eliminate or reduce the number of out-of-travel motions in a part program and avoid collision events (when VM simulation is present) by selecting an initial pose that avoids an overtravel or collision during the cutting process.
Minimize the number of rotary turn-around (RTA) events (see “Rotary Turn-Around”) by selecting an initial pose that maximizes the initial cut length.
Pre-position singular axes on a positioning or cutting motion, to avoid dwell marks caused when a rotary must be rotated in place at the start of a motion (see “Singular Pre-Positioning”).
Optimize the winding of rotary axes with limited travel in excess of 360 degrees (see “Rotary Winding”), by reducing or eliminating out-of-travel motions or RTA events.

LPP performs these optimizations by scanning forward in the part program to the end of the current tool path (defined as a positioning motion or any LINTOL command) and using this analysis to apply an optimal 5-axis pose at the start of the tool path. LPP is controlled as follows:

$\textbf{LINTOL / SCAN},\textbf{ON} \; \big[,\textbf{MAXDPM},\ldots \big]\; \big[,\textbf{OPTION},n \,\big]$

$\textbf{LINTOL / SCAN},\textbf{OFF}$

OFF disables LPP. ON enables LPP. An LPP scan begins when a RAPID or high feed positioning motion is encountered. LPP scans forwards through all subsequent positioning motions and then through the entire feed interpolation tool path, analyzing the motions so as to generate an optimal initial positioning move.

If RAPID linearization is active, then a LINTOL/TLANG,OFF condition (see “Tool-Tip-Only Linearization”) must be in effect to give LPP the flexibility to change from one rotary axis pose to another during the positioning move. Otherwise, GENER will be forced to choose a single rotary path, which negates the effectiveness of LPP. If a rotary axis is moved during a high feed positioning motion, then the feed motion will be tool-tip-only linearized, regardless of the LINTOL/TLANGL setting.

$\big[,\textbf{MAXDPM},\ldots \big]$

see “Singular Pre-Positioning” for a description of the MAXDPM option.

$\big[,\textbf{OPTION},n \,\big]$

When there is a sequence of two or more positioning motions at the start of a tool path, LPP by default applies the pose change on the positioning motion that has the longest lateral component. This default can be changed by coding a modal OPTION,n value as follows:

1

SCAN,NEXT during longest lateral move (default)

2

SCAN,NOW at start of longest lateral move

3

ROTREF,NEXT during longest lateral move

4

ROTREF,NOW at start of longest lateral move

11

SCAN,NEXT during first positioning move

12

SCAN,NOW at start of first positioning move

13

ROTREF,NEXT during first positioning move

14

ROTREF,NOW at start of first positioning move

21

SCAN,NEXT during highest positioning move

22

SCAN,NOW at start of highest positioning move

23

ROTREF,NEXT during highest positioning move

24

ROTREF,NOW at start of highest positioning move

Because LPP can cause the machine to move from one pose to another on the initial positioning motion, it is important to program positioning motions well clear of the part. In particular, options 11 and 12 should be used with caution as they will result in a rotary pose change while in contact with the part when the first positioning move starts in contact with the part.

As with RTA, LPP passage can be replaced by SmartPATH generated safe and optimal positioning sequence.

Forced Path-Planning Scan

LPP analysis can be activated at a specific location using the following commands:

$\textbf{LINTOL / SCAN}, \begin{pmatrix}\,\begin{array}{l} \textbf{NEXT} \\ \textbf{NOW} \end{array}\,\end{pmatrix}$

$\textbf{LINTOL / ROTREF}, \begin{pmatrix}\,\begin{array}{l} \textbf{NEXT} \\ \textbf{NOW} \end{array}\,\end{pmatrix}$

With either of these commands, an LPP analysis is performed and a pose change is performed only if necessary.

With SCAN,NOW the pose change occurs in place at the current tool tip position. With SCAN,NEXT the pose change occurs on the motion to the next tool position. Use the SCAN method when the tool is well clear of the part.

With ROTREF,NOW the pose change occurs in place at the current tool tip location using a rotary turn-around (RTA) motion (see “Rotary Turn-Around”). With ROTREF,NEXT the pose change also uses a rotary turn-around, retracting from the current position and plunging at the next tool position.

The NOW and NEXT options do not change the ON or OFF state of LPP. If LPP is disabled, the NOW and NEXT options cause a one-time analysis. If LPP is enabled, the NOW and NEXT options simply define specific locations (overriding any default or specified OPTION value) where an LPP pose change should be applied if required.

Please note that forced LPP may not be always possible. LPP avoids overtravel or Collision on a 5-axis machine by selecting one of the two available kinematics paths, selecting the one that features no interference. It may happen that at current position the desired kinematic solution is not available (out-of travel or it would collide the machine). This is why it is always better to run SCAN,ON method allowing post processor to choose the best position where LPP rotation should be applied.

Singular Pre-Positioning

A rotary axis is said to be singular when the axis of rotation is parallel to the tool axis. In this case, the orientation of the rotary axis has no effect on the orientation of the tool with respect to the part. As an example, a typical machine C rotary axis will be singular when the tool is in either a (0,0,1) or (0,0,–1) orientation.

Linearization path planning and rotary turn-around both include logic that test for the case where a rotary axis is singular at the start of the cutting sequence. GENER will look forward in the feed interpolation block looking for the first motion that forces the singular rotary axis to a specific angle. This rotation is then output during the positioning sequence before cutting starts, to avoid dwell marks caused by rotating the rotary axis in-place during cutting.

GENER also provides an option to similarly test for singular pre-positioning while cutting. In this case, the test checks for the case where a rotary axis goes from a non-singular to a singular condition during cutting. GENER can look ahead in the cutting tool-path for the next feed motion that forces the singular rotary axis to a specific angle and then carefully apply the rotation during the cutting sequence to avoid rotating the axis in place.

Singular pre-positioning while cutting is controlled by including the MAXDPM keyword option on the LINTOL/SCAN command[1]:

$\textbf{LINTOL / SCAN},\ldots,\textbf{MAXDPM} \begin{pmatrix} \!,\! \begin{array}{l} \big[\,\mathit{low},\big]\,\mathit{high} \\ \;\textbf{ON} \\ \;\textbf{OFF} \end{array}\,\end{pmatrix} \begin{bmatrix} ,\! \begin{array}{l} \textbf{START} \\ \textbf{END} \end{array}\,\end{bmatrix}$

The low and high values specify the range of rotary axis rotation speeds (in degrees per minute) to use when a singular rotary axis is pre-positioned. The default maximum high rate is the physical rotary axis limit. The default low rate is half the maximum. GENER will attempt to rotate the axis at a speed as close as possible to the low end of the range. GENER will segment a motion, if possible and if necessary, to avoid exceeding the maximum rotation rate.

START specifies that the singular pre-positioning should happen in the motions immediately after the rotary axis goes singular. END (the default) defers the singular pre-positioning to the motions immediately before the rotary axis goes non-singular (i.e., is needed).

Rotary Winding

Rotary axis winding is a process that winds (i.e., backs up) a rotary axis on a positioning motion, so as to extend the range of travel available during the cutting motions. Winding works in combination with linearization path planning (LPP) and rotary turn-around (RTA), but only on machines that have one or more rotary axes with “range” travel limits of 360 degrees or larger

Winding is controlled by the following command:

$\textbf{LINTOL / WIND}, \begin{pmatrix}\,\begin{array}{l} \textbf{ON} \\ \textbf{OFF} \end{array}\,\end{pmatrix}$

OFF (the default) disables rotary axis winding. ON enables winding. When winding is active with LPP, GENER will rotate (i.e., wind) a rotary axis as much as is necessary or possible on the positioning motion, so as to avoid an overtravel condition on that rotary axis during the cutting process. When winding is active with RTA, GENER will do the same on the lateral orientation shift motion.

Winding can produce positioning motions that include multiple full revolutions of one or both rotary axes. However, winding only rotates these axes by the minimum amount necessary to avoid or limit out-of-travel conditions for the upcoming tool path.