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KEB Technology

VFDs for theatre applications

Jonathan Bullick | July 23rd, 2015

KEB variable-frequency drives come in a variety of housings and power levels and have a large catalog of options that make them well suited to operating motors in theater and stage applications. Here are some of the features you can look for in KEB VFDs for theatre and stage applications..


Quiet operation

As with theatre brakes and gearmotors, it’s often required that drives (or VFDs) be as quiet as possible when operating during a performance.


The high frequency PWM switching of an inverter creates audible noise. Lower performance drives which operate at 4kHz create noise right where the human ear is most sensitive. Some manufacturers standardize on lower switching frequencies because it reduces IGBT heating and allows for higher ratings. Also it is easier to control and requires less power processors.


KEB’s F6 VFD and S6 servo drive have adjustable carrier frequencies and are capable of running up to 16kHz. 16kHz is in a range less sensitive to the human ear and virtually silent A nice feature with KEB’s drives is that the carrier frequency automatically derates if needed for momentary increased current capacity.


Communication protocols

KEB drives offer a wide range of communication options which allow them to be integrated into many different master controls. All S6 drives come with a native EtherCAT slave hardware and include ProfiNet, Powerlink, and EtherNet/IP options.


theatre ethercat servo drive
The S6 Servo Drive offers complete flexibility


A big advantage to using KEB’s new generation of drives is that one drive platform covers all different control platforms. If a person chooses (or is forced) to use different PLC vendors, all that changes is the hex addresses and bus related parameters.



Dual encoder channels

KEB’s drives feature dual encoder channels which can be configured as inputs or outputs. This gives the opportunity for the KEB drive to evaluate multiple encoder signals and evaluate for error scenarios. One possible implementation is to compare the high speed motor feedback and speed feedback from the drum side of a theater winch.

vfd encoder input
The S6 servo drive features dual channel feedback


The KEB drive can then evaluate the two signals, scale for gearing ratio and determine if an e-stop needs to be made. Encoders can be installed by KEB per the customer’s direction during manufacturing, or an encoder kit can be used to re-fit the drive as needed.


The F6/S6 drives utilize a multi-format high density input which supports all different formats from one hardware.



Lifting overhead loads or powering rigging that will support actors requires safety as the top feature. As standard, the S6 servo drive includes Safe-Torque-Off (STO) and Safe-Brake-Control (SBC) functionality. Extra safety functionality according to ISO 13849 is available for the S6, including: SS1, SS2, SOS, SLS, SLP, SLI, SDI, SSM. STO functionality can be added as an optional feature to other KEB drives. The functionality is approved by a 3rd party safety agency.


Functional safety over EtherCAT (FSoE) is especially interesting for theatre applications. FSoE allows much of the safety wiring to be handled over the bus. It is possible that discrete safety wiring can be replaced with a network cable.


This simplifies wiring at the jobsite and improves the ability to get diagnostics and troubleshoot the network. All 6th generation drive products (S6/F6) have an option for FSoE.

fsoe servo drive
FSoE allows networked safety


Besides functional safety offerings, KEB drives also have a number of internal parameters and functions that can be used monitor and detect abnormal operating situations (e.g. slackline or broken gearing) and react accordingly.


Push through heat sink

F5 VFD In Theatre Application
This image shows a KEB F5 VFD in use in a theatre setting. The drive features a push through heat sink along the left side, and can accommodate a brake resistor (seen here between the cabinet and gearmotor) for dissipating heat generated by the machinery.

During operation VFDs product heat. Larger drives which produce more heat require larger panels or more complex cooling options. This sometimes conflicts with the space constraints placed on theatre hoist machinery and their electrical enclosures.


KEB offers several heat sink options, including a push through design. KEB’s push through drives allow the heatsink to be placed outside the panel. In this configuration, about 80% of the drives heat is dissipated outside the enclosure which allows for a much smaller enclosure to be used.


Everything onboard

The amount of space machinery takes up is frequently a concern in theatre and stage applications. KEB drives have several components fully integrated into the drive to reduce the number of individual components needed.


Distributed control can be achieved with the built-in positioning capability of the drives, allowing for precise multi-axis control without the need of an expensive master controller. A master control could provide a set position to the drive through the communication bus and the drive handles the position profile.


The drives also have integrated low leakage EMI filters and brake transistors rated to 100% of rated current. In addition to saving on space, these features add to the overall noise-reduction and energy savings of the drive.


KEB – A partner for Theatre Technology

Contact a KEB application engineer and let’s discuss how to create some cutting edge theatre controls.

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