To Improve a Motion

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To Improve a Motion

Improve the Motion

This is a very subjective problem. A good motion for one application may not be a good motion for another.

An attempt to answer...


The motion is for a machine, and not a cartoon character.

The motion is intended for a machine where the machine elements reciprocate, oscillate, index, or the speed modulates in some way.

General Advice:

If possible, use the Flexible Polynomial Motion-Law for all of the segments in your motion. This motion-law has the most motion-design flexibility.

Remove Velocity discontinuities.

Remove Acceleration Discontinuities, in nearly all machine design circumstances

Always ask yourself “Can I reduce the number of segments?” Use a minimum number of segments.

Always ask yourself “Can I delete a Dwell Segment?” Try to remove Dwell Segments - especially short dwells. Usually it is better to remove a Dwell segment, and give the adjacent segments zero velocity, acceleration and jerk.

Reduce the number of motion-specifications.

E.g. You can make a motion continuous in position, but do not control the actual position at a Blend-Point.

Try to make the peak acceleration values of each segment similar to each other, or try to give similar motion durations.

This is not always possible or desirable. But consider balancing the motion to give similar motion durations or peak accelerations, or both.

Can you increase the distance a part is moved but give it a little more time.

Why select different Motion-Laws?

A motion-law might:

give more flexibility for you to control the motion-derivatives at the Blend-Points

suit the mechanical system. For example, the motion-law might have a 'low peak maximum velocity'.

give a good dynamic response to the mechanical system. For example, the motion-law might have a good response to system backlash, low drive stiffness.

agree with a company preference(!) - for example Modified Sinusoid is often a company preference.

However, I nearly always design my motions with Flexible-Polynomial segments as they give me almost all of the flexibility I need.