Trapezoidal spindles and the Theater Pforzheim – how do they fit together?

Trapezoidal Spindles and theater stage? At first glance, they seem unrelated. However, upon closer inspection, the curtain rises above the stage. Anyone who's been to the theater knows that during intermissions, the theater stages are usually transformed. Either the stage is rotated, or parts are changed using a different stage profile. But how does this work in detail, and why's the transformation so quick? Let's take a look under the theater stage.

Underneath the theater stage lies a complete lifting system. It can easily consist of 100 or more lifting drives, universal joints, distribution gears, and a control system. To ensure the stage set can be variably changed, the lifting system must be designed so that the necessary torque reaches even the last lifting drive of the system. This is where GROB Antriebstechnik comes into play as a specialist in linear drives.

What exactly does the Trapezoidal Spindle do in the theater?

The Theater Pforzheim features, among other things, an innovative lifting system that raises a 5-meter-high, floor-retractable shelf. This shelf serves as storage for various stage parts and is an essential component for the smooth operation behind the scenes. At the heart of this innovative system are 4 Trapezoidal Screw Spindles TR70x10. With the help of these four Trapezoidal Screw Spindles, the theater staff can precisely and reliably raise and lower the shelf to bring the corresponding stage parts onto the theater stage. After the performance, the stage parts are lowered again and disappear beneath the stage.

Why the choice fell on us when 4 Trapezoidal Spindles had to be replaced

For Gerhard Reule, the managing director of Reule & Sons Hydraulics - Pneumatics OHG, who rebuilt the system, the matter was clear: "It was important for me to have someone who produces in the region and can also provide personal advice directly at the facility. Of course, you could also buy the drives cheaper in Italy, but what if a problem arises then? I've had very good experiences with GROB - both in technical consultation and in on-site service."

By the way, we hear this from our customers again and again. They appreciate the personal and competent advice. They know that we react quickly to inquiries and can also deliver quickly. And that we also react immediately in the event of a service case and don't leave the customer out in the rain.

For Theater Pforzheim, one aspect was particularly important in the collaboration: the safety of the system. How can a lifting system be secured so that accidents are excluded? From our point of view, there are two ways to ensure safety in operation:

1) By self-locking of the trapezoidal spindle

Self-locking is the ability of the Trapezoidal Screw Spindle to maintain its position even without power supply. This means that the spindle cannot rotate or lower under load, preventing uncontrolled dropping of the stage elements. And that means safety.

This is an important safety aspect that prevents uncontrolled lowering of the shelf. The Trapezoidal Thread as a motion thread has relatively high friction. This means that the screw spindle in the area of the control thread is self-locking, which has the advantage that it doesn't need to be additionally secured in the rest position.

Generally, the limit for self-locking is at an efficiency of 50%:

1. Below 50% efficiency, self-locking can be assumed with certainty.
2. Above 50% efficiency, self-locking is conditional, insecure, and with increasing efficiency finally no longer given.

The limit of dynamic self-locking is at 28% efficiency:

1. From 28 to 50% efficiency, there's static self-locking, with decreasing effect towards 50%, here caution is particularly required with vibrations and shocks, and the different deceleration when switching off the drive must also be observed.
2. Below 28%, dynamic self-locking can be assumed with certainty. Here, it may even be possible to dispense with brakes, as the system stops immediately when the drive is switched off.

If you want to calculate a Trapezoidal Screw Spindle with nut yourself, you will find the corresponding calculation formulas in the formula collection in our catalog on page 189.

2) By a safety nut

The safety nut (SFM) normally runs load-free with the worm wheel. In case of a bearing nut breakage, the SFM takes over the load. A lift can still be performed to stop the system. The SFM also serves as a reference nut for permanent wear measurement and thus for predictive maintenance. Monitoring can be done optically or electrically.

What should be considered when planning a lifting system in stage construction?

The planning of such a lifting system requires careful consideration of various aspects. These key points need to be identified:

1. Needs analysis: What are the requirements for load capacity, size, stroke length, speed, and functionality?
2. Space planning: How large is the available space including the travel range? Are there any restrictions? What are they?
3. Safety: What safety aspects need to be considered? Emergency stop, stability, fall protection, personnel protection, potential hazards.
4. Maintenance: Plan regular maintenance and inspection work to ensure the long-term functionality and safety of the lifting platform.

Success Story in Stage Construction

This success story illustrates how GROB and the Theater Pforzheim, through their collaboration, found an innovative solution for a complex challenge faced by a theater stage. It's an example of how technical expertise and creative thinking can work together to achieve impressive results in linear drive technology. And it's evidence that at GROB, the customer is always at the center. Because at GROB, it's not just about delivering components, but solutions that make a difference.

Thomas Kricheldorf, machine technician at Theater Pforzheim, is entirely satisfied: "Everything worked out perfectly," he reports, and continues: "The material arrived neatly packaged and precisely fitting. We were able to install the spindles and the main and follow-up nuts according to plan, and now everything's working optimally and flawlessly again."

What else you should know about GROB Antriebstechnik

Since 1945, our family-owned company has been developing and producing solutions for linear drive technology. Our solutions can be found around the globe. In our product portfolio, you'll find Screw Jacks, Spindle Lifting Gears, Spindle Drives, Linear Drives, Trapezoidal Screw Spindles, MINI Actuators, Linear Chains, and a whole range of special solutions that we've developed for specific application cases.