9/Series CNC Lathe. Operation and Programming Manual

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

If the last programmed move is circular (an arc), the tool is positioned at

right angles to a tangent line drawn from the end-point of that circular

move.

Figure 21.21

Tool Path for Exit Move Arc-to-Straight Line

G39 (Linear Generarated Blocks)

G39.1 (Circular Generated Block)

£q£90

End-point

G42

Programmed path

G41

G42

G41

£q£180

G42

G41

180

£q£270

End-point

Programmed

Path

Programmed path

End-point

G39 (Linear Generated Block)

G39.1 (Circular Generated Block)

270

£q£360

G42

270

£q£360

G42

Programmed path

G41

End-point

12117-I

21-27

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.20 and Figure 21.21 assume that the number of blocks that do

not contain axes motion in the currently selected plane, following G40

before the exit move takes place, do not exceed an amount selected in

AMP by your system installer. If the number of non-motion blocks

following G40 exceeds the limit, the control generates its own exit move.

This may often cause overcutting of the part, since this move is a linear

path directly back to the programmed tool path.

You can modify the path that the tool takes for an exit move by including

an I- and/or K-word in the exit move. Only the I- or K-words that

represent values in the current plane are programmed in the block

containing the exit move. I and K correspond to the X and Z axis

respectively.

The I- and K-words in the exit move block define a vector that the control

uses to redefine the end-point of the previously compensated move.

The vector defined by the I- and/or K-words is along a line drawn from the

end-point of the programmed path through a point programmed with the I-

or K-words. The I- and/or K-words must be in the currently defined plane.

The point defined by I and K is always one incremental distance from the

end-point of the last move measured parallel to the X and Z axis.

A new vector is then defined parallel to the vector defined by the I- and/or

K-word and offset from this vector in the direction and amount of the

currently active offset (G41 or G42). The intersection of this new vector

with the current compensated tool path defines a point which is the new

end-point of the last programmed compensation move.

Figure 21.22

Exit Move Defined By An I, K Vector

Compensated path using I, K vector

Compensated path if no I, K in G40 block

Intercept line

I, K

Compensated path

Programmed path

Figure 21.22 is the exception. The change in length of the compensated

path is more than one radius of the tool. In this case, this offset is limited

to one radius of the tool. The direction of the offset is towards the point of

intersection of the I and/or K vector and the current compensated tool path.

21-28

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Example 21.10

Exit Move Defined By An I, K Vector But Limited To Tool Radius

Assume T1 radius is 3.

N10 Z10.G41T1;

N11 X10.Z2.I3K-10.G40;

Figure 21.23

Results of Example 21.10

Compensated path using I, K vector

Compensated path if no I, K in G40 block

N11

Compensated path

Programmed path

N10

I, K

Intercept line

If the vector defined by I and/or K is parallel to the programmed tool path,

the resulting exit move is offset in the opposite direction of the I, K vector

by one tool radius.

Figure 21.24

Exit Move When I, K Vector is Parallel to Programmed Tool Path.

Compensated path using I, K vector

Compensated path if no I, K in G40 block

Compensated path

Programmed path

Intercept line

I, K

Important: If one I and/or K value is programmed without the second one,

the value of the second I- and/or K-word defaults to 0.

21-29

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

21.5

Except for entry and exit moves, the basic tool path generated during

TTRC is the same for types A and B TTRC. Whether tool left or tool right

Tool Path During TTRC

is specified, the path taken is a function of the angle between tool paths

(G41 or G42) and the radius of the cutting tool.

Important: If at any time during the execution of TTRC blocks a block

reset is performed, the TTRC function re-initializes and the next move acts

as an entry move as described in an earlier section.

Important: When cutting arcs with TTRC active, the control may need to

adjust the programmed feedrate to maintain cutting speed. See chapter 18

for details on feedrates during TTRC.

The control generates extra motion blocks to keep the cutting tool in

tolerance of the desired tool path. This becomes necessary when the

intersection of tool paths is an outside tool path (as defined in section 22.1)

that has an angle as follows:

between 0°and 90°during TTRC left (G41)

between 270°and 360°during TTRC right (G42)

21-30

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.25 through Figure 21.28 illustrate the basic motion of the cutting

tool as it executes program blocks during TTRC.

Figure 21.25

TTRC Tool Paths Straight Line-to-Straight Line

G39 (Linear Generated Block)

G39.1 (Circular Generated Block)

Linear

£q £90

generated block

Circular

generated block

G41

Programmed path

G42

£q £180

180

£q £270

G41

Programmed path

G41

Programmed path

G42

G39 (Linear Generated Block)

G39.1 (Circular Generated Block)

270

£q £360

270

£q £360

Circular

generated

Linear

block

generated

block

G41

Programmed path

G42

12121-I

21-31

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.26

TTRC Tool Paths Straight Line-to-Arc

G39 (Linear Generated Block)

G39.1 (Circular Generated Block)

£q£90

Linear

generated

Circular

blocks

generated

block

Programmed

path

G41

G42

G41

G42

£q£180

180

£q£270

G41

Linear

generated

block

Programmed

path

G41

G42

Programmed

path

Linear

G42

generated

block

G39 (Linear Generated Blocks)

G39.1 (Circular Generated Block)

270

£q£360

270

£q£360

G42

G41

G42

G41

Programmed

path

Linear

Circular

generated

blocks

block

12122-I

21-32

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.27

TTRC Tool Paths Arc-to-Straight Line

G39 (Linear Generated Blocks)

G39.1 (Circular Generated Block)

£q£90

Linear

Circular

generated

blocks

block

Programmed

path

G41

G42

G41

G42

Linear

£q£180

generated

180

£q£270

block

Programmed

path

Programmed

path

Linear

generated

block

G41

G42

G41

G42

Linear

generated

Circular

G39.1 (Circular Generated Block)

G39 (Linear Generated Blocks)

270

£q£

360

blocks

270

£q£360

generated

block

Programmed

path

G41

G42

G41

G42

12123-I

21-33

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.28

TTRC Tool Paths Arc-to-Arc

G39 (Linear Generated Block)

G39.1 (Circular Generated Block)

£q £90

G41

Programmed

path

G42

£q £180

180

£q £270

G41

Programmed

path

G41

G42

Programmed

path

G42

G39 (Linear Generated Block)

G39.1 (Circular Generated Block)

270

£q £360

270

£q £360

Programmed

path

G42

G41

12124-I

21-34

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

21.6

The following subsections describe possible tool paths that can be

generated when programming one of the following during TTRC:

TTRC Special Cases

changing TTRC direction (cross-over tool paths)

exceeding the allowable number of consecutive, non-motion blocks

during TTRC

corner movement following a generated block

changing cutter radius during TTRC

effect on TTRC when interrupting a program to execute either a MDI

program or a manual move

changing or offsetting current work coordinate system during TTRC

moving to and from machine home and secondary machine home

21.6.1

This section describes the resulting tool path when a change in

compensation direction (left or right) is programmed. This can result in

Changing TTRC Direction

the cutting tool crossing over the programmed tool path as compensation

changes from left to right or right to left.

Linear Tool Path-to-Linear Tool Path.

The following figures show the tool path taken when TTRC is changed

from G41 to G42 during the execution of two linear program moves.

The control generates two points when changing TTRC direction: point 1

and point 2.

Point 1 is the final tool position before compensation direction is

changed (at right angles to the end-point of the programmed tool path

offset by one tool radius)

Point 2 is the desired tool position for the start of the first block using

the changed compensation direction (at right angles to the start-point of

the motion block that changes compensation direction and offset by the

tool radius)

21-35

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

The control generates the motion block that connects point 1 to point 2 as

shown in these examples:

Example 21.11

Linear-to-Linear Change in TTRC Direction (Reversing Tool Path)

N10 Z10.G41;

N11 Z20.;

N12 Z10.G42;

N13 Z0.;

Figure 21.29

Results of Example 21.11

Point 1 & 2

Compensated

N10

Programmed G41

N11

N13

Programmed G42

N12

Example 21.12

Linear-to-Linear Change in TTRC Direction (Continuing Tool Path)

N10 Z10.G41;

N11 Z20.;

N12 Z30.G42;

N13 Z35.;

Figure 21.30

Results of Example 21.12

Point 1

Compensated

Programmed G41

G41

G42

N10

N11

N12

N13

Point 2

21-36

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Example 21.13

Linear-to-Linear Change in TTRC Direction (With Generated Blocks)

N10 X15.Z10.G41;

N11 X-5.Z8.;

N12 X0.Z35.G42;

Figure 21.31

Results of Example 21.13

N11

Compensated

path

N10

Programmed

path

G41

N12

G42

Point 2

Point 1

Example 21.14

Linear-to-Linear Change in TTRC Direction (No Generated Blocks)

N20 X5Z10.G41;

N21 X-5.Z7.G42;

21-37

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.32

Results of Example 21.14

Point 2

Point 1

Compensated

path

N20 (G41)

Programmed

path

N21 (G42)

For one of these cases that changes the TTRC direction, the control

attempts to find an intersection of the actual compensated tool paths:

Linear-to-Circular, Circular-to-Linear, or Circular-to-Circular Tool Paths

If the control finds an intersection, it modifies the end-point of the original

compensated tool path and the start-point of the new compensated tool

path to equal that intersection. See Figure 21.33.

Figure 21.33

Change in Compensation with Actual Tool Path Intersection

G42

G41

Programmed G42

Programmed

path

Compensated

path

Compensated

path G41

Compensated path G41

Programmed path

G42

If no intersections of the actual tool paths exist, the compensated tool path

is the same as if a linear-linear intersection had taken place. See

Figure 21.34.

21-38

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.34

Change in Compensation With No Possible Tool Path Intersections

Compensated path

r₂

r₁

Programmed path G41

G42

r₁

r₂

Programmed path G42

Compensated path

G41

Compensated path

Programmed path G41

G42

21.6.2

The control always looks ahead to the next motion block to determine the

actual tool path for a motion block in TTRC. If the next block is not a

Too Many Non-Motion

motion block, the control continues to scan ahead for a motion block until

Blocks

it either detects one or the allowable number of non-motion blocks as set in

AMP has been exceeded. Refer to documentation prepared by your system

installer for the allowable number of non-motion blocks allowed in a

specific system.

Important: The definition of a non-motion block is any block within a

program that does not actually generate the movement of one of the axes in

the current compensated plane. Blocks that are skipped by the control

because of the block skip feature (/) are also counted as a non-motion

block in TTRC, regardless of the content of the skipped block.

21-39

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

When scanning ahead, if the control does not find a motion block before

the number of non-motion blocks has been exceeded, it does not generate

the normal TTRC move. Instead the control sets up the compensation

move with an end-point one-tool radius away from and at right angles to,

the programmed end-point. In many cases this may cause unwanted

overcutting of a work piece.

In many cases, this can cause unwanted overcutting of a work piece.

Figure 21.35 and Figure 21.36 are example tool paths of programmed

motion blocks followed by too many non-motion blocks before the next

move was made.

Figure 21.35

Too Many Non-Motion Blocks Following a Linear Move

Too many

non-motion

Compensated

blocks here

path, G41

Compensated

path, G41

Programmed

path

Programmed

path

Compensated

path, G41

Programmed

Too many

Programmed

non-motion

path

blocks here

Compensated

path, G42

Too many

non-motion

End-point of compensated

blocks here

move if not too many non-mo-

tion blocks

21-40

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.36

Too Many Non-Motion Blocks Following a Circular Move

Programmed

path G42

Programmed

path G42

Compensated

path

Compensated

path

Too many non-motion

Too many

blocks here

non-motion

blocks here

Programmed

path G42

Compensated

path

Too many

non-motion

blocks here

21.6.3

Frequently the control must generate motion blocks to position the cutting

Corner Movement After

tool in the proper alignment for a following compensated cutting move.

These blocks are generated to make certain that the cutting tool remains at

Generated Blocks

least one radius of the cutting tool away from the programmed cutting path

at all times.

When the control generates two motion blocks, the length of the first

generated block is checked against a minimum allowable length as

determined in AMP by your system installer. The coordinate values for the

current axes in the compensation plane are compared to the minimum

allowed value. If both are less than the allowed value, then the control

does not executes the first generated block. The path of the second

generated block is then altered to position the cutting tool along a linear

path to the original end-point of the second generated block. See

Figure 21.37 for a pictorial representation.

21-41

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.37

Compensation Corner Movement for Two Generated Blocks

This block is eliminated if both

X₁Z₁

hX₁-X₂h and hZ₁-Z₂h are

less than AMP parameter

New block if block

is eliminated

X₂Z₂

Compensated

Programmed

When the control generates 3 motion blocks, the length of the second

generated block is checked against a minimum allowable length,

determined in AMP by your system installer. The amount of motion of the

second move on the two axes in the compensation plane is compared to the

minimum allowed value for each axis. If both are less than the allowed

value, then the control does not execute the second generated block. The

path of the third generated block is then altered to position the cutting tool

along a linear path to the original end-point of the third generated block.

See Figure 21.38 for a pictorial representation.

Figure 21.38

Compensation Corner Movement for 3 Generated Blocks

New block if block from X₁ Z₁

to X₂ Z₂ is eliminated

This block is eliminated if both

| X₁-X₂ | and | Z₁-Z₂ | are

X₁ Z₁

less than AMP parameter

X₂ Z₂

21-42

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

21.6.4

If a tool becomes excessively worn, broken, or for any other reason

requires the changing of the programmed tool tip radius, TTRC should be

Changing Cutter Radius

cancelled and re-initialized after the tool has been changed. See page

During Compensation

NO TAG on changing the tool offset and page on changing the active tool

offset number.

Important: Slight overcutting may occur during Cutter Compensation,

depending on the programmed path at the point where the change in cutter

radius was made. To avoid overcutting, we recommend that you use a

Mid--Start Program until the point of tool breakage.

Figure 21.39 through Figure 21.41 are representations of the resulting tool

paths after the programming of a change in the radius of the cutting tool.

Assume in these figures that the programmed change to the tool radius is

entered in block N11 which also contains the motion as described in the

figure.

The tool path taken when changing tool radius is dependant on the move

immediately before the change in radius was programmed, the move that

the change in radius was programmed in, and whether any generated

motion blocks were made between these tool paths.

Figure 21.39 gives a description of the tool path when the programmed

moves are linear-to-linear.

Example 21.15

Linear-to-Linear Change in Cutter Radius

When the control generates blocks

When the control does not generate

blocks

N10 X10.Z5.G1T1;

N10 X10.Z10.G1T1;

N11 X-5.Z3.T2;

N11 Z20.T2;

N12 Z20.G42;

N12 X0.Z30.;

21-43

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.39

Linear-to-Linear Change in Cutter Radius During Compensation

With control generated

No control generated

motion blocks

N10

Generated

N11 D_

blocks

N12

r₁

r₂

Compensated

r₁

N10

path

r₂

Compensated

r₂

N11

path

N11

r₂

Programmed

N10

N12

path

N12

Figure 21.40 describes the tool path when the programmed moves are

linear-to-circular.

Figure 21.40

Linear-to-Circular Change in Cutter Radius During Compensation

No control generated

With control generated

motion blocks

Generated blocks

Programmed

Compensated

path

r₁

Programmed

r₂

path

Compensated

r₂

path

r₂

21-44

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.41 describes the tool path when the programmed moves are

circular-to-circular.

Figure 21.41

Circular to Circular Change in Cutter Radius During Compensation

No control-generated

With control-generated

motion blocks

Programmed

path

Programmed

path

Compensated

path

r₁

path

r₂

r₁

r₂

Generated blocks

Change in Cutter Radius During Jog Retract.

This section concerns a change in the cutter radius during a jog retract

operation. The jog retract feature is often used when a tool becomes very

worn or is broken. It can be necessary to replace the tool with a tool of a

slightly different diameter. TTRC is able to adjust to the new tool

diameter.

Typically when the jog retract operation is performed, the tool is jogged

away from the workpiece and then replaced. After it is replaced, you need

to activate a different tool diameter offset value. This is done in either of

two methods:

The new offset number is activated by programming a new D-word in

an MDI block.

The new offset number is activated by using the {ACTIVE OFFSET}

softkey found on the offset table screen. This feature is described in

chapter 3.

21-45

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

The new offset is activated. TTRC is able to compensate for this new

diameter by modifying the saved jogged path. This path is modified so

that the new tool cuts the same part as the old tool. The absolute position

of the machine will, therefore, be different on the return path from what it

was when jogging away from the part.

This jogged path is adjusted when you press the <CYCLE STOP> button

to return from the jog retract. As soon as you press the <CYCLE STOP>

button, the control generates a move that offsets the current tool position

by the necessary distance. This distance is determined as the necessary

distance the tool where would have to be positioned so that the exact same

jog return paths can be used to return to the part and still have the

end-point be offset from the original position by the difference in the cutter

diameter.

CAUTION: Make sure that this offset path will not cause any

collisions with the part or the machine fixtures. The position of

the tool when the tool change in jog retract is made should be a

safe distance from the part and machine fixtures.

21-46

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.42 shows an example of a typical change in tool radius during

jog retract with TTRC active:

Figure 21.42

Change in Cutter Radius During a Jog Retract

Programmed path

Original tool

radius

New tool

Compensated path

radius

Difference in

90°

Jog retract moves

tool radius DR

Jog retract

return moves

Tool radius

changed here

Generated offset block

from difference in

tool radius DR

21.6.5

If exiting automatic mode and either a MDI motion block is executed or a

manual jog motion is made, the TTRC feature, if active, will be

MDI or Manual Motion

re-initialized when the next motion block is executed. The compensation

During TTRC

feature compensates the cutting tool one tool radius perpendicular to the

tool path of the next motion block that is executed in automatic mode. In

effect, the control generates its own entry move for compensation with the

first compensated block being the next block executed in automatic

operation.

Important: The TTRC feature is not available for any motion blocks that

are programmed in MDI mode. The TTRC mode may be altered by

programming either G41, G42, or G40, or the tool radius can be changed

in an MDI program. However, none of the tool paths executed in MDI will

be compensated. Any changes made to TTRC will not be applied until the

next block executed in automatic mode.

Figure 21.43 is an example of the possible tool path taken when

interrupting automatic operation during TTRC to execute MDI motion

blocks. The same tool path would apply if interrupting TTRC to perform a

manual jog move.

21-47

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.43

TTRC Interrupted with MDI Blocks

3 MDI blocks

(no compensation

applied)

Programmed path

G42

End-point

of MDI

Compensation

reinitializes here

Important: If during cutter compensation, you switch out of automatic

mode and either:

generate axis motion in manual mode on an axis in the cutter

compensation plane, or

execute any block in MDI mode,

cutter compensation is re-initialize when you return to automatic mode.

This produces a path that is different from the path that would have been

produced had the manual or MDI operation not been done, even if you

returned the tool to the point of interrupt. In absolute mode the control

returns to the originally compensated path after it executes a block that

contains both axes in the compensation plane. In incremental mode, the

compensated path remains offset by the additional tool radius.

Figure 21.44 illustrates these conditions.

21-48

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Figure 21.44

Cutter Compensation Re-Initialized after a Manual or MDI Operation.

Cutter Compensation is re-initialized here. The control assumes that the

current position is a programmed position at the point of re-initialization.

Consequently, after the initialization, tool compensation is offset by twice the

tool radius.

Manually jog axes (or any MDI

execution) and return to the

compensated path.

Over Compensated Path

(after MDI/Manual Interrupt)

Original Compensated Path

(had no interruption occurred)

Tool Radius

Programmed Path

Use the Jog Retract feature if you must jog the axes away from a

compensated path. Jog retract prevents the overcompensation from

occurring.

If you interrupt cutter compensation with a manual or MDI operation and

the next programmed block is a circular block, the control generates an

error when it tries to re-initialize cutter compensation. You can avoid this

by using the jog retract feature instead of manual or MDI when you need

to interrupt cutter compensation.

Unless Cutter Compensation is active, when a program recover is

performed, the control automatically returns the program to the beginning

of the block that was interrupted. In the case of power failure, the control

will even reselect the program that was active prior to the interruption.

21.6.6

We recommend that you cancel TTRC by using a G40 command before

Moving To/From Machine

executing a return to, or from, machine home, or a return to or from the

secondary machine home. This refers to the operations performed when

Home

the control executes either the G28, G29, or G30 commands as described

in chapter 14.

If compensation is not cancelled by using a G40 command, the control

automatically, temporarily cancels compensation for the return to machine

home or secondary machine home operations. This done by using the

move to the intermediate point, as designated when the operation was

performed, as an exit move for compensation.

Important: An intermediate point should always be programmed for a

return to home operation if TTRC is active. If no intermediate point is

21-49

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

specified, the control executes the move prior to the return to home

operation as an exit move. This can cause undesired overcutting of the

part.

If compensation was not cancelled using a G40 command before returning

to machine or secondary home points, the control automatically

re-initializes TTRC for the return from machine or secondary home points.

This is done by using the move to the intermediate point, as designated

when the operation was performed as an entry move for compensation.

Figure 21.45 shows either a G28 or G30 block followed by a G29 block:

Figure 21.45

TTRC During G28, G30, and G29 Blocks

G41

Programmed

path

N14’

N11

N12

N15

N13

Temporary cancel of

compensation here

N13’

N14

at intermediate point

Reference point

21-50

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

21.6.7

We recommend that you cancel TTRC by using a G40 command before

any modifications to the current work coordinate system are made,

Changing or Offsetting Work

including any offsets or any change of the coordinate system (G54-G59.3).

Coordinate System in TTRC

If compensation is not cancelled using a G40 command, the control

automatically, temporarily cancels compensation for the change in work

coordinate system. This is done by using the last compensated move in the

current coordinate system as an exit move for compensation.

If compensation was not cancelled by using a G40 command before a

change in the work coordinate system was performed, the control

automatically re-initializes TTRC after the new work coordinate system is

established. This is done by using the first move in the new coordinate

system that is in the compensation plane as a entry move for compensation.

Figure 21.46 gives an example of programming a G92; however, this

would apply to any change in the work coordinate system.

Figure 21.46

TTRC During G92 Offset to Work Coordinate System

G41

Programmed

path

N14

N10

N11

N15

N12

N13

Temporary cancel of

compensation here

21-51

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

21.6.8

During normal program execution, the control is constantly scanning ahead

several blocks to set up the necessary motions to correctly execute the

Block Look-Ahead

current block. This is called Block Look-Ahead.

The 9/Series control has 21 set-up buffers. Different features require the

use of some of these setup buffers. One is always used for the currently

executing block. TTRC requires at least 3 of these buffers. Any remaining

setup buffers are used for block look-ahead, with one buffer used for each

block.

At times (especially during TTRC) the control may not have enough

look-ahead blocks to correctly execute the current block. When this

happens, the control automatically starts disabling the block retrace

feature.

The block retrace feature uses one setup buffer for every re-traceable

block. The number of re-traceable blocks is set in AMP by your system

installer (a maximum of 15 is possible).

If necessary, the control decreases the number of available re-traceable

blocks until either there are sufficient setup buffers available to

successfully execute the current program, or until there are no more block

retrace blocks left. The control displays a message on line 2 of the CRT if

it has to eliminate some of the block retrace blocks.

Avoid using too many buffers for block retrace. The larger the number of

look-ahead blocks that the control has available to set up future part

program motion requests, the more efficiently the control executes

programs. We recommend that you keep the number of setup buffers

available to the block retrace feature as low as possible.

21.7

Error detection for TTRC blocks can be separated into 3 categories:

Error Detection

Backwards motion detection

Circular departure too small

Interference

21-52

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Backwards Motion Detection

The compensated tool path is parallel to but in the opposite direction of the

programmed tool path.

Figure 21.47

Typical Backwards Motion Error

Compensated

Programmed

Path

D’

A’

C’ B’

Compensated path

motion opposite of

programmed path

Circular Departure Too Small

No intersection can be generated between two consecutive compensated

tool paths.

Figure 21.48

Typical Circular Departure Error

Compensated

path

Error is generated

because compensated

paths do not intersect

Programmed

path

Compensated path necessary

to cut arc

21-53

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Interference

This error occurs when compensation vectors intersect. Normally when

this intersection occurs, a backwards motion error is generated; however, a

few special cases exist that are caught only by interference error detection.

Figure 21.49

Typical Interference Error

Error is generated because

compensated vectors cross

Compensated path

necessary

to cut arc

Compensated path

Programmed path

12145-I

Disabling Error Detection

You can disable all of the above error detection (with the exception of

circular departure too small cases) for a specific block or portion of a part

program. To disable the error detection for a specific block, your system

installer must have defined an M-code in AMP. By programming this

M-code in a block, all error detection for TTRC can be disabled. Error

detection is disabled until another M-code defined in AMP to re-enable

error detection is programmed in a block.

Important: Circular departure too small cases cannot be disabled. The

control cannot execute a compensated path when this error occurs.

The default condition is error detection enabled. Default values for these

M-codes are:

M-code:

Error detection:

M800

disables

M801

enables

21-54

Chapter 21

Tool Tip Radius Compensation (TTRC)

Function

Error detection M-codes are only functional when TTRC is active. TTRC

is active when the control is in G41 or G42 mode and has already made

the entry move into compensation. If an M800 or M801 is programmed

in G40 mode or before the entry move into TTRC takes place, the M code

is ignored.

If error detection is disabled in TTRC, and TTRC is exited (G40

programmed), the next time TTRC is re-activated error detection will be

re-activated automatically. Error detection is always automatically enabled

when cutter compensation is activated.

Refer to documentation prepared by your system installer for the M-codes

used on your specific system.

END OF CHAPTER

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9/Series CNC Lathe. Operation and Programming Manual - page 18