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SimpleMotion AntiSwing

SimpleMotion AntiSwing is an innovative hardware and software system that allows precise control of stage elements such as LCD displays, set pieces, lighting rigs etc to track both horizontally and vertically without pendulum effects. This allows designers to realise their creative visions and venues to support outstanding shows and events.


Below is a short demonstration video...


At Simplemotion we support the capability to minimise swing for hung loads. When a load is suspended and is driven in a lateral way, the load has the freedom to swing when the move is finished. This can be a serious problem for lifting applications as well as a visual problem for theatre.

Recently, antiswing algorithms were implemented on the Sydney Theatre Company production of The Picture Of Dorian Gray to prevent excessive swing on large LED screens that are suspended from trusses. These screens were moved both up and down and left to right, sometimes simultaneously, which called for sophisticated algorithms to reduce the swing.


We can separate the problem of swing into 2 categories- Horizontal and XY.


Horizontal Antiswing

Firstly, if the screen is moving horizontally only, then we can use a specific, effective algorithm to reduce the swing to effectively zero. The algorithm calculates the period of the natural pendulum swing of the object and counteracts it by precisely calculating the move acceleration and deceleration phases.


XY Antiswing

To remove or reduce swing in 2 planes, horizontal and vertical, a more sophisticated algorithm is required. The base algorithm is a multi-parameter PID loop that optimises for the final move position and the estimated swing angle. Additionally, we have created an optimisation stage that optimises for certain move characteristics that can be prioritised. The metrics considered are:

  • Diagonality- how diagonal should the XY move be- do we care about the axes moving in tandem in a diagonal trajectory?

  • Velocity Symmetry- is it acceptable for the move to spend a lot longer on the deceleration than the acceleration phase to compensate for swing?

  • Residual swing- what is an acceptable amount of swing?

  • Exact Move Time- is it important to complete the move within a certain time?

To find the correct move parameters simulate a PID control loop that minimises swing and various other factors and optimise for the metrics that we consider the most important to ensure that the trajectory produced meets the requirements.

The capability exists to completely eradicate swing from a move; however, this will result in a trajectory that may not be suitable for certain applications.

Once a particular move is created, we can repeat it easily using the Simplicity Command Motion system.

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