Motion Control & Drives


Limit switches for show-stopping performance

January 2023 Motion Control & Drives

A well produced theatre experience is capable of entrancing the audience to the point that the members are fully immersed. Ironically, this means that most theatregoers fail to appreciate the engineering required to move the lights, scenery and props that contribute to a memorable performance. One general contractor ensures that its stage equipment is positioned precisely where it is required, thanks to Stromag Series 51 limit switches.

Behind the scenes

Installed above the stage of many theatres is the upper machinery − mostly winches and hoists driven by motors. These winches and hoists raise and lower lights, scenery and props to support the performances of the actors on stage, providing extra atmosphere and immersion for the audience. However, with a multitude of heavy equipment operating above the performers, it is imperative that loads stop exactly where needed with total reliability.

One stage equipment business applies the latest theatrical technologies to deliver large-scale installation projects, a particular area of expertise being upper machinery. The contractor often relies on Series 51 geared cam limit switches from Stromag, a leading brand of Altra Industrial Motion, to ensure precise and reliable stopping for upper machinery.

Reliable stopping

Marco Niehnus, global product manager of Controls at Stromag, explains: “The upper machinery in theatres is similar to a crane application, with loads being moved up and down. Ensuring that these loads stop reliably is critical for the safety of performers on stage below. Our Series 51 geared cam limit switches set the upper and lower stopping points of these loads by accurately measuring the number of shaft turns, delivering highly reliable stopping performance.”

This reliability is evidenced by the TUV DGUV V17 certification held by the Series 51. This is the German quality standard for upper machinery used in theatres and TV studios. While not a legal requirement globally, many customers follow this standard to ensure that upper machinery equipment offers the utmost reliability. As a result, the Series 51 is a popular selection for stage applications in Japan, Australia, Russia, Europe and the USA.

The Series 51 is suitable for many upper stage machinery configurations. This includes fly bar drives, which feature a lifting device with steel wires wound around a single drum and attached to a bar or traverse; tubular shaft drives, where each wire is wound around its own drum and can move multiple bars; as well as point hoists, which feature a single wire for lifting. The limit switch can be installed to measure the turns of the motor or the winch drum, ensuring versatility.

Precise performance

“Precision and ease of adjustment are key advantages of the Series 51,” Niehnus adds. “The stopping points can be set with a simple worm gear, which when turned, moves the cam disc and actuates its switching position. A cam disc gear ratio of i=146 means that it takes 146 turns of the worm gear to fully rotate the cam disc. This ensures incredibly precise adjustment for the contractor’s requirements.”

While this level of precision may seem excessive, this high gear ratio actually makes it easier for users to set an exact stopping point. Limit switches with lower gear ratios offer a reduced accuracy for setting stopping points due to the less available points per rotation, making it difficult to find the optimum position. Conversely, the more accurate Series 51 allows fine adjustments to be carried out easily – ideal for stopping scenery, props or lighting in exact positions.

Proven on stage

“Over the years we have worked with this stage equipment contractor, we have built a strong technical relationship. They provide us with detailed information regarding the applications and the number of turns to our local team, and we deliver Series 51 limit switches to the required gear ratio. This ensures we can offer a solution precisely to their requirements on a project-by-project basis,” Niehnus concludes.




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