Gearing

LabVIEW 2017 SoftMotion Module

Edition Date: March 2017

Part Number: 371093V-01

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Gearing allows one slave motor to be driven in proportion to a master motor or encoder. As the slave follows the master position at a constant ratio, the effect is similar to that of two axes mechanically geared.

Electronic gearing has several advantages over mechanical gears. The most notable is flexibility because you can change gear ratios on-the-fly.

An axis can be geared to another axis or to an encoder. When you gear an axis to another axis, the slave axis follows the trajectory generation of the master axis. For example, if you manually move the master axis, the slave axis does not move because the trajectory generator of the master axis is not active.

Note Note  Do not attempt to perform "circular gearing" in which the master and slave are both geared to each other as a double master/slave pair. Doing so may result in unexpected behavior, including causing the axes to stop responding to commands after executing a move.

You can use any basic move type on the master axis and slave axis responds according to the specified gear ratio, including straight-line moves, arc moves, and contour moves. You cannot perform a reference move on a slave axis with gearing enabled.

When you gear an axis to an encoder, the slave axis follows the feedback generated by the encoder. If the encoder detects movement, the slave moves proportionally to information returned by the encoder. For example, if you twist the master axis connected to the encoder, the slave axis also turns because it is using the position information gathered by the encoder.

The SoftMotion Module uses relative, rather than absolute, gearing. This is most important when applying new gear ratios in the middle of a move or sequence of moves. With absolute gearing, new gear ratios are applied to the absolute encoder position. For example, if the master axis is at 1,000 counts and the gear ratio is 2:1, the slave axis is at 2,000 counts. Changing the gear ratio to 4:1 results in the slave axis immediately jumping to 4,000 counts even though there has been no motion from the master axis. This could cause jerky behavior and position error. Relative gearing applies the new ratio relative to the current position, preventing sudden jumps and position error.

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