CANopen sinks a building for James Bond - continued
The equipment designed to control the rig centered on an M3000 system, which for this application can be split into the hardware — Moog Servo Controller (MSC); and software — Moog Axis Control Software (MACS). It was used to control six digital Axis Control Valves (ACV), which, in turn operated six hydraulic actuators. Feedback of the actuator position was achieved using a number of wire-driven encoders supplied by the partner company. The digital nature of all of the hardware was a major selling point according to Dan Stanton at EMP Designs who states, ”With respect to the hydraulic control, we have worked with other companies in the past, but we wanted to do something special this time. Moog was the only company that could supply what we wanted — a hydraulic system based on digital valve technology”.
Dan Stanton continues, ”The digital approach offered us finer control and it also gave us more confidence when it came to the safety aspects as, if anything were to get disconnected or the control was lost, we knew about it as it gets detected immediately. Much of the actuation was also performed in synchronized pairs so digital also gave us far greater control in this respect. Another vital consideration was the amount of radio frequency that exists on film sets, and given the long cable lengths digital is far more resilient so we were less prone to external influences in the control and feedback loops.”
In the application the MSC controller used a CAN link to connect to six ACVs, each of which controlled a cylinder — working in pairs, this gave three axes of motion. The ACVs then used a CANopen network to connect to the BTF encoders, which produce a unique digital code for every 0,025 mm of travel — providing the precise feedback required for cylinder position. The ACVs provided remote closed-loop position control for each degree of motion. This reduced the processing load on the MSC allowing it to take care of the safety monitoring and synchronization. The MSC provided all the profile generation for the ACVs over the CANopen network. ”This was a new approach for us but the M3000 offered us a stable, flexible control structure and cost-effective solution for what we were trying to achieve,” continues Stanton. ”It also offered the capability for us to integrate a 38,1-cm touch-screen (HMI), which gave us a complete simplistic overview of the system using MACS (Moog Axis Control Software) — which, as well as offering us clear visualizations, allowed us to pinpoint the source of any erroneous readings.
”One important aspect of the software was that it allowed the system to self diagnose,” Stanton explains. ”We were able to create routines that would highlight any discrepancies or anomalies. This was the first time we had ever used a controller that helped us make the decision of whether to press the ‘big red stop button’; if anything deviated it was able to assess the severity and then make a decision based on this figure — it took a lot of the worry out of it for us. The controller also incorporated a ‘Watchdog’, which reverted to a safe state should any issues arise with the controller.”
”There are some very big movies in production at the moment which are also using this technology,” Stanton continues. ”Indeed there has been significant interest from the movie world with many production companies expressing an interest in what we can do with this digital system. The flexibility of the M3000 system is that it is also designed for electro-mechanical actuation, this allows us to look at other types of film effects including smaller scale animations using small DC motors; once again it is the software that pays dividends. We also have to consider the fact that movie concepts can change over night so flexibility is vital — this is another benefit the digital approach gives us.”
