Relevant block length
The minimum curve length is limited because of the mathematical resolution of the control (given by the number of significant digits of a REAL64-value and the procedure). At the moment this length is 15,85 micrometers. Path segments less than this minimum curve length causes an error message and the abortion of contouring.
Additionally, the contour can include very short compensation blocks, created by a programming system (CAD/CAM) or by a tool radius correction. This blocks after correction should ensure a continuous form of the path.
To avoid an abortion of contouring at these short blocks, it is possible to define a minimum block length, from which the polynomic contouring is relevant for the next block. Shorter blocks are ignored during active contouring and the contouring considers the following block.
It can be defined a limit for the movement distance of the main axes as well as a limit for the movement distance for the tracking axes. The block is skipped completely only if both, the movement distance of the main axes and the movement distance of the tracking axes is under the defined limit. The polynomial contouring combines the previous and the following block curvature and direction continuous. The basic blocks must not border on each other (contour must not be continuous).
If a block is skipped, now the maximum corner deviation of the main axes and the tracking axes is only approximately considered. This means, it is supposed, that the skipped blocks concerning the deviation of the contouring can be ignored.
Programming example
#CONTOUR MODE [DEV, PATH_DEV 5, RELEVANT_PATH 2]
N03 G01 X0 Y0 Z0 C0 F4
N907090 G04 X0.1
N04 X5 G261
N05 Y1
N09 X10 Y3 G260
N907091 Y0
Special case 1: Sequence of multiple short blocks behind the block transition
If multiple sequential blocks (N20, N30, N40) are shorter than the minimum movement distance, these blocks are skipped if the distance of the target position to the last relevant end position (N10) is shorter than the defined minimum movement distance. If the target position of the skipped block is outside the enclosing sphere, this block (N40) is used for the calculation of the contour curve, even if it is shorter than the defined minimum length. This method enables a small deviation from the original contour even if multiple sequential blocks are skipped.
Special case 2: Sequence of multiple short blocks behind the block transition, last block is extremely short
As a special case the block N40 itself can be shorter than the minimum system specific length (about 15 micrometers) required for the contouring. In this case the last end position and the new target position is connected by a linear block. This new linear block N20´ then is used for the calculation of the contour curve.
Special case 3: Short blocks before the block transition
If at the beginning of contouring (before block transition) the blocks are already shorter than the minimum length given by the system, these blocks are skipped. The blocks are skipped if the distance between the last valid position and the current target position exceeds the minimum block length. If this is the case, the last end position and the current target position is connected by a linear block N10. This linear block then is used as start block for contouring.
Special case 4: Deselection of contouring or change of parameterisation.
If contouring is deselected during skipping of blocks or the basic conditions for contouring are changed, the current contouring may only be continued until the deselection or parameter change. After that the contouring possibly can be continued with the new parameters.
