This site contains a two and one-half minute video clip highlighting a kinetic sculpture/machine that continuously ties and unties a necktie. Although it is artistically inspired and intended for entertainment, the machine, (name "Why Knot"), dramatically demonstrates how engineering principles and methods can be used to solve unusual problems not normally associated with technology.
The sculpture consists of a necktie hung from a platform located above an array of ten electric motors placed at strategic locations in the space near the tie. Different actuators, e.g. levers, pulleys, sliders, bicycle crank/sprocket/chain, winch, each attached to a motor shaft, move and manipulate the necktie to tie the knot providing graphic examples of mechanical devices in action. A computer outputs a sequence of numbers to electronic circuits that convert these numbers into voltages that control the ten motors. Both the circuitry and a monitor displaying the control numbers are visually prominent. The "brains" of the machine consists of the sequence of number pairs that determines which motor moves how far, and in what order to finish he task. After the necktie is tied, the knot is pulled apart so it can begin again. The video contains an especially amusing part in which the cycle is filmed at ten times normal speed.
For those interested in some of the technical details, the overall process is open loop. Each motor is a DC gearhead unit configured as a closed loop servo using a shaft potentiometer to provide feedback to its own power amplifier whose input is a separate sample and hold circuit. The first of the computer provided number pairs controls which of the sample and holds is strobed. The second of the two numbers is fed to a digital to analog converter whose output is simultaneously available to all the sample and holds, but is only "seen" by the unit which is strobed. Actuators move at the slew rate of each motor until they approach their commanded position.
I would be happy to correspond to interested parties about any aspect of the sculpture. I can be reached at: Seth Goldstein, Sc.D
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