Siemens CNC Milling | G09-G60-G64 | Exact Stop/Continuous-Path Control Mode

Function Introduction

G functions are provided for optimum adaptation to different requirements to set the traversing behavior at the block boundaries and for block advancing. For example, you would like to quickly position with the axes or to machine contours over multiple blocks.

Codes Format

Exact Stop

G09 ; Exact stop non-modally effective
G60 ; Exact stop modally effective
G601 ; Exact stop window fine
G602 ; Exact stop window coarse

Continuous-Path Control

G64 ; Continuous-path mode

Exact Stop Details

If the exact stop function (G60 or G9) is active, the velocity for reaching the exact end position at the end of a block is decelerated to zero.

Another modal G group can be used here to set when the traversing movement of this block is considered ended and the next block is started.

G601; Exact stop window fine
Block advance takes place when all axes have reached the “Exact stop window fine” (value in the machine data).

G602: Exact stop window coarse
Block advance takes place when all axes have reached the “Exact stop window coarse” (value in the machine data).

The selection of the exact stop window has a significant influence on the total time if many positioning operations are executed. Fine adjustments require more time.

See the following illustration for exact stop window coarse or fine, in effect for G60/G9:

Exact Stop Example

N5 G602 ; Exact stop window coarse
N10 G0 G60 X20 ; Exact stop modal
N20 X30 Y30 ; G60 continues to act
N30 G1 G601 X50 Y50 F100 ; Exact stop window fine
N40 G64 X70 Y60 ; Switching over to continuous-path mode
N50 G0 X90 Y90
N60 G0 G9 X95 ; Exact stop acts only in this block
N70 G0 X100 Y100 ; Again continuous-path mode

Note: The G9 command only generates exact stop for the block in which it is programmed; G60, however, is effective until it is canceled by G64.

Continuous Path Control Mode Details

The objective of the continuous-path control mode is to avoid deceleration at the block boundaries and to switch to the next block with a path velocity as constant as possible (in the case of tangential transitions). The function works with look-ahead velocity control over several blocks.

For non-tangential transitions (corners), the velocity can be reduced rapidly enough so that the axes are subject to a relatively high velocity change over a short period of time. This may lead to a significant jerk (acceleration change). The size of the jerk can be limited by activating the SOFT function.

Continuous Path Control Example

N10 G64 G1 X10 Y20 F1000 ; Continuous-path mode
N20 X30 Y30 ; Continuous-path control mode continues to be active
N30 G60 Z50 ; Switching over to exact stop

Look-Ahead Velocity Control

In the continuous-path control mode with G64, the control system determines the velocity control for several NC blocks in advance automatically. This enables acceleration and deceleration across multiple blocks with approximately tangential transitions. For paths that consist of short travels in the NC blocks, higher velocities can be achieved than without look ahead.

See the following illustration for comparison of the G60 and G64 velocity behavior:

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