Influencing of look-ahead functionality (G115/G116/G117)
G115 General influencing of look-ahead functionality (modal)
G116 Influencing of calculation of block-transition rate-velocity (modal)
G117 Resetting of look-ahead functionality (modal, default)Overview of the functionality of Look-ahead-function
Within the Look-ahead-function different single functions are implemented, limiting the traversed speeds to maximum values, thus the permissible axis speeds and axis accelerations can always be maintained.
The following single functions influence the speed profile:
- Calculation of the maximum path speeds on the basis of the maximum axis speeds, specified in channel parameters list[1]-26.
- The speed on the programmed path should thus be limited that each of the axes participating in the movement does not exceed their maximum axis speed.
- Calculation of the maximum path speeds on curved paths on the basis of a maximum chord error.
- For this purpose, on each curve at the point of the most pronounced curvature, the curve radius can be determined. On this circle a circular section can also be defined, which beginning, and end point correspond to the generated point. Under the condition that the real mechanical system would move on the respective chord, the relevant height of the circular section can be included as the error criterion.
- Calculation of maximum path speed on curved paths on the basis of the maximum axis acceleration specified in channel parameters list[1]-26.
- The maximum path speed calculated based on the secant error can still be too high, particularly in shorter tracing time and smaller circular movements, so that the resultant centripetal accelerations would exceed the permissible axis accelerations.
- Calculation of the path transition speed on the basis of the block-transition geometry, taking into account the axes taking part in the movement and their limit values specified in channel parameters list[1]-26.
- During a block transition, generally, the respective proportion of the individual axes alternate in the total movement. This change of the axis condition occurs however only in the first tracing cycle on the new path (linear movement). If it is pre-supposed that the transition should take place without the generated acceleration (for instance by the slope-function), an estimation of the resultant axis accelerations can be undertaken. Thus, the calculation of a maximum path speed at block transition is possible, in which, the maximum axis accelerations will not be exceeded at transition.
General case: Normal operation with look-ahead
After program start all functionality of the look-ahead is switched on (G117). Thus, it is ensured that parameters given in the axis data block, such as for example maximum axis acceleration, are always observed.
Special case: Disconnection of single functions of the Look-ahead-function through G115
Programming example
Nnn G115 = 0 (Switching off the single
functions 2,3 and 4)(of Look-ahead-funct.)In the following table the possible combinations of the single functions are explained.
 | The correspondingly selected or deselected functions always refer to all the axes. |
Survey of permissible identification numbers (ID) accompanying G115:
Einzelfunktion | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
0 | * |
|
|
|
2 | * |
|
| * |
4 | * | * |
|
|
6 | * | * |
| * |
8 | * |
| * |
|
10 | * |
| * | * |
12 | * | * | * |
|
14 | * | * | * | * |
*Single function active | ||||
Programming example
Nnn G115 = 2 (Switching off individual functions (2) and (3))
Nnn G115 = 12 (Switching off individual function (4))
Nnn G115 = 14 (Switching on of all individual functions after)
(program start, see also G117)Special case: Influencing of look-ahead functionality by G116, G117
By G116 the calculation of the block transition speed is switched off for individual programmable axes. No reduction in the block transition speed (path speed) takes place because of "corners" in the path.
| In this case the dynamic axis data (axis accelerations) will be exceeded normally. |
Programming example
N10 G116 X1 Y2 (No decrease in block transition rate of)
(different axis speeds of the axes X or Y)
N20 G01 G91 X100 Y-100 F1000
N30 X-100In this example block transition N20/N30 is traversed without set speed infringement. The command values are changed a the block transition in form of jumps according to the part of the path of the axis.
Notice | |
The coordinate value is required only for syntax reasons and is irrelevant otherwise |
By G117, all the single functions of Look-ahead-function become active (default setting after program start) again.
Programming example
Nnn G117 (Switching on all single functions (1),(2),(3),(4))
(of Look-ahead-function)