Automation and Art: Kinetic Sculpture Relies on Synchronized Servos

Kinetic Rain sculpture at Singapore’s Changi Airport uses PC-based control and EtherCAT to synchronize movement of 1,216 servo axes.

In our coverage of automation applications, we typically focus on industrial applications of various automation technologies. But uses for automation extend beyond the practical, production-oriented needs of industry. Increasingly, we are seeing industrial automation technologies employed to make our lives fun and exciting through their use in entertainment productions, at amusement parks, and through artistic applications.

A recent example of an artistic application of industrial automation can be found in Terminal One of Singapore’s Changi Airport. Mimicking the movement of tropical rain, the Kinetic Rain sculpture consists of 1,216 copper-plated aluminum droplets suspended from the ceiling on thin steel wires. The sculpture is composed of two contiguous fields of 608 droplets each, extending over a total area of more than 800 square feet. A small servomotor controls the movement of each droplet in the sculpture’s 15-minute show. During the show, the droplets form into different dynamic shapes connected by the theme of flying.

Berlin agency Art+Com developed the concept; technical implementation and programming were handled by MKT AG from Olching, Germany. Beckhoff Automation supported MKT AG during the programming and implementation of the sculpture’s control system built using Beckhoff Automation’s products.

High requirements were set for the kinetic sculpture where dynamics, precision and speed of the motion sequences were concerned: The droplets move with a speed of 1.5 m/s and an acceleration of 1.4 m/s²; their movements had to be dynamic, flowing and free of any jerky movements.

Moving the 1,216 servo axes synchronously to designers’ specifications is handled using Beckhoff’s EtherCAT industrial Ethernet technology, TwinCAT automation software and compact EL7201 EtherCAT Terminals that function as servo drives.

A C6525 industrial PC is responsible for control of the sculpture. It communicates via TwinCAT ADS (Automation Device Specification) with a specially designed GUI computer from MKT. The PC centrally controls the 1,216 axes via TwinCAT NC PTP and acts as the master. Via TwinCAT’s cam table function, the master PC coordinates the distribution of the position data to six slave PCs, which each are assigned 192 or 208 axes and ensures the synchronicity of all axes according to a master axis as reference.

The GUI computer from MKT is used for visualization, but also contains the show in the form of a table, ensuring the position data for each droplet at time intervals of 200 ms, corresponding to five shapes per second. A flowing movement perceptible by the human eye without jerks is made possible through interpolation in TwinCAT NC PTP. In this controller, 100 intermediate positions are calculated for each droplet using a spline algorithm in a 2 ms NC task. These calculations take place on each slave PC for the local axes assigned to it. While the master keeps all the axes synchronous to one other, the slave PCs calculate the positions of the axes assigned to them every 2 ms and communicates over EtherCAT in real-time to the servo drives.

According to Axel Haschkamp, director of MKT AG, the movement of the individual axes is extremely precise and lies in the range of 1 mm for an overall length of around 25 ft. The maximum offset between two droplets is 0.25 mm. Each droplet is controlled via an EL7201 EtherCAT servomotor terminal and AM3121servomotor from Beckhoff. “In the servo terminals, we found an extremely compact solution that fit the structural conditions with limited installation space in the ceiling of the building,” he says.

“Also important for us was the modular implementation of the control solution and the fact that an individual axis can be exchanged without addressing. That made partial commissioning possible [in that] we were able to work in parallel on software, hardware and the mechanism, allowing us to keep within the narrow timeframe that we had for this project,” Haschkamp says.

Using the TwinCAT NC PTP it was possible to “jog” Kinetic Rain’s show (i.e., fast forward and/or rewind it) to simplify commissioning. If an individual path of the sequence was not satisfactory, the engineers from MKT could repeat it continuously until it was correct. “With other solutions this was not possible and we would have been forced to continually start the show from the beginning each time until we reached the desired position, which would have been very time consuming,” says Haschkamp.

Watch a video of the Kinetic Rain sculpture in action at the Changi Airport below.

Companies in this article
More in Control