Contour with tangential block transitions

An abrupt change in the acceleration and high jerk takes place at the block transition from linear to a circular block or at the transition from a circle to a circle with a radius change or a direction of rotation also change the path velocity is kept constant. Related to this behavior in the following a few examples are shown with velocity, acceleration, and jerk in axes.

1.Block transition linear block -> circular block

2. Block transition circular block -> circular block with direction of rotation change G03 -> G02

3. Block transition circular block -> circular block with radius change r2 !=r1

Parameterization

The permissible jerk at tangential block transitions is weighted by the P-AXIS-00154 parameter.

By means of the value 0, the influence of this parameter changes to jerk limitation, and the weighting of the permissible acceleration with the cycle time/ramp time factor applies. Thus, the corresponding axis jerk is kept to the permissible limits in accordance with the ramp time parameters P-AXIS-00195..- P-AXIS-00198 and the acceleration parameters P-AXIS-00011 and P-AXIS-00012. The resulting speed at the tangential block transition is very low.

j = (P-AXIS-0004 / tr)*(P-AXIS-00154) / 1000. _trans

With the value 1000, (upper limit) the parameter has the lowest influence to block transition velocity. The jerk at block transition is relatively high and can be estimated by ratio of current active acceleration and cycle time.

A value > 0 may make sense whenever it is undesirable for technological reasons for the contouring speed to drop depending on the set jerk at block transitions with a constant tangent.

A value < 1000 may make sense if machine structure is vibration sensitive, has vibrations or oscillations and there is no technology process problem resulting because of relatively small velocity on block transitions with constant tangent.

The jerk limitation at tangential block transitions has to be activated explicitly via channel parameter P-CHAN-00009.

The influence of jerk imitation to path velocity of linear and circular contour with constant tangent is shown below, supposing that the path velocity in circular contour is reduced because of permissible axis acceleration.

Path velocity

- without jerk limitation at block transition

- with jerk limitation at block transition

Parameter example for jerk limitation at tangential block transition:

Jerk limiting:

Excerpt from the channel parameter list:

corr_v_trans_jerk    1

Excerpt from the axis parameter list:

getriebe[0].dynamik.a_trans_weight    0
getriebe[0].dynamik.r_trans_weight    0

no jerk limiting:

getriebe[0].dynamik.r_trans_weight    1000
getriebe[0].dynamik.a_trans_weight    0

Excerpt from the channel parameter list:

corr_v_trans_jerk    0

If contour deviation is allowed, then contour modifying functions e.g. polynomial contouring can be used to get shorter processing time and lower path velocity variations at block transitions. In this case, in general higher block transition velocities can be driven with active jerk limitation at non tangential and tangential contour definition. This is shown in the diagram below with the example of non-tangential block transitions. The knee angle of this block transition is 1 degree. In contrast to block transition velocity without polynomial contouring the block transition with polynomial contouring can be driven with higher velocity although the contour error is kept relatively small.