Tow tank control system upgraded to Couch Carriage

The Aaron Friedman Marine Hydrodynamics Lab manned carriage control system has completed a comprehensive upgrade thanks to an establishing gift by John Couch (NAME BSE MSE) in honor of his late father, Richard B. Couch. Couch spent a decade as Chair of UM’s Naval Architecture and Marine Engineering Department (1957-1967) and remained a close friend and supporter of NAME until his passing. The tow tank carriage will now be named The Couch Carriage in his honor. 

The much-needed upgrades to the existing system were established when the prior controls system began having operational outages due to failures in the control PC’s power supply and cabling.  An assessment of the existing system showed that the architecture of the controls system was incompatible with a simple swapping of the control PC, as well as several areas for major improvement in maintainability and upgradability if the system were to be replaced wholesale.  

The implementation of the new controls system allows also for an upgrade to the aging drive system.  All four drive-shafts were rebalancing and refurbishing and the gearboxes and servomotors were all replaced.  The down-time for these upgrades provided an opportunity also to install fully shielded stainless steel conduit runs for each of the four servomotors’ power and controls cables, significantly reducing the electromagnetic interference the motors produced in the various instruments on the carriage during testing.

To further improve the comfort and communication level of the carriage’s occupants, the pneumatic emergency brake’s air compressor was replaced with a new ultra-quiet compressor.  This new compressor allows for communication to continue uninterrupted during its operation, something that was impossible with the original system.  

The old controls cabinet’s supporting brackets were removed and replaced with additional and more substantial brackets that were welded in-house by one of the hydro lab’s interns, Lyn Tran.  The new support brackets sport several easter-eggs for any keen observer and pay homage to the student interns (fondly referred to as “tank rats”) that make the MHL’s operations possible.  

With the new controls cabinet installed, a representative from the system’s designer and builder, Van Halteren Technologies, arrived from the Netherlands to run the newly installed system through its paces including;  proportional-integral-derivative (PID) tuning of the servomotors’ drives to ensure a smooth ride, verification of the on-board real-time safety control logic, as well as a full testing of the physical back-up safety systems.  The most dynamic of these rigorous commissioning tests were the maximum acceleration and deceleration tests, which saw the carriage undergo runs at various acceleration and deceleration rates to check for wheel slip on the rail.  

With the new system commissioned and the staff fully trained on its operation, the new carriage controls and drives will allow the Aaron Friedman Marine Hydrodynamics Laboratory to continue to use the 120-year-old towing tank for cutting-edge testing in the marine sphere for decades to come.  The new system is a programmable logic controller (PLC), which is the industry standard for industrial automation and robotics systems throughout the world.  This new architecture will allow for quick and robust updates and upgrades to the carriage’s control capabilities for many years into the future.

In addition to the vast increase in serviceability and upgradability, the new system comes with several additional layers of safety.  The old system precalculated a motion profile and checked it against a single positional encoder before allowing the carriage to move.  The new system does this and checks each servomotor’s encoder and calculates the ability to safely stop in real-time during each run.  There are several additional layers of safety controls programmed into the system as well as physical limit switches installed on the rails to ensure that the carriage will always stop safely. 

An official commissioning ceremony for the new Couch Carriage will take place on April 19, 2024, at 11:30.