Animation Case Study
Oregon Electric: Smooth Moves for a Dancing Blowfish
How do you control the motion of a large mechanical object when it needs to move smoothly and spontaneously, as though it was alive? This challenge is tackled by engineers who design attractions for theme parks. To create the illusion of lifelike motion, they must avoid the jerky movements of old-fashioned robots -- remember C3PO from the Star Wars adventures? -- and must provide the ability to choreograph that motion with music or coordinate it with other goings-on in the show.
Michael Curry Design, Inc. of St. Helens, OR, a specialist in costume mechanics, needed to create a 175 pound, 12 foot long mechanical blowfish as one of the prominent actors in a mermaid show at an Asian theme park scheduled to open next year. Raising and lowering the fish from the theater ceiling in a manner that simulates swimming, synchronized to a music track proved to be a challenge. Simple electric hoist controls provided by Allied Power Products, Inc. of Beaverton, OR were not designed to provide the lifelike motion required, so Allied brought in Oregon Electric Group of Portland, OR, a specialist in electrical system design with over 1000 employees in Oregon and Washington. Oregon Electric chose the RMC100 motion controller from Delta Computer Systems of Vancouver, WA to control the lifelike swimming motion of the giant blowfish.
Primary control inputs to drive the vertical swimming motion of the fish are provided in the form of two 0-10V infinitely-variable analog signals generated by a show control computer from Gilderfluke (Burbank, CA). The Delta RMC100 interfaces directly to the analog signals (two signals, one for the fish's head and one for its tail), smoothes them to filter out noise, and drives two Allen-Bradley servo drives and motors to raise and lower the ends of the fish. The position of the servos is sensed via quadrature encoder inputs to the RMC.
Easy to program, smooth moves
A key requirement of the motion controller was that it be easy to program and that programs be easy to change as the show performance is refined. The task of programming the RMC controller involved controlling relatively high rates of acceleration and deceleration to move the mass while avoiding jerkiness. A graphical development package from Delta called RMCWin facilitated programming and tuning of the motion. RMCWin allows the system designer to plot on his computer screen how closely the system's actual motion matches the target motion.
Setting up a motion profile on the RMC is done by entering parameters into a motion sequence table that specify how the two axes are to move in response to the analog input signals. Then, using the graphical tools, the designers can home in on the optimal motion profile very quickly. If a change to the motion profile is needed, making the change is as easy as updating the motion table with new command values. Control equation coefficients like the P, I, and D (proportional, integral and derivative) factors that govern how motion outputs respond to sensor inputs can be changed on the fly as the system operates.
The Delta motion controller also receives digital inputs to support system safety features, insuring that the motion of the fish will remain within safe bounds, no matter what the levels of the analog input signals are. Other digital I/Os support manual operation of the head and tail during servicing and maintenance operations.
"The Delta controller is very user-friendly," stated Jeff Curry, engineer for Michael Curry Design.
"I'm an electrician, not a motion control expert," explained Dan Heinze of Oregon Electric Group. "But I was able to complete the application with only two weeks' effort spread over a period of 4 or 5 calendar weeks." In addition to programming the motion controller, Oregon Electric Group built the control cabinet housing the motion controller and drive control electronics in their UL508 listed panel shop. "We especially appreciated the small size of the Delta RMC controller because it was easy to fit into the control cabinet," added Heinze.
Although most motion control engineers aren't creating giant dancing fish, almost any application can benefit from easy programming and the ability to generate smooth motion. Selecting the right motion controller can provide big benefits.