Kinetic frame needs new backers

Frame was developed for use in spinal surgery and could also be used for advanced medical chairs and airline seating

The inventor of a form-changing space frame that can adjust its shape to provide optimal support in a number of possible applications has appealed to the engineering community to help scale-up the technology.

The kinetic frame, which comprises telescopic linear actuators and free-rotation joints, has been developed for use in spinal surgery and could also be used in applications including advanced medical chairs and airline seating, moving theatre sets and advertising displays.

Architect Paul Harkin has been partnering with Imperial College London to produce a variable-geometry platform for surgical tools, effectively a low-cost but precise hexapod manipulator, which was first demonstrated publicly at the IEEE Robio 2014 conference in Bali in December.

Harkin, founder of Form Changing Structures, said: “It was well-received. But I want to develop a bigger, multiple-module frame to demonstrate the novel and more complex applications like seating. 

“Crucially, I need a collaboration partner, such as a precision engineering company I can work with to make 50 to 100 of the modules. I need to make them lighter, cheaper and easier to manufacture.”

The rods are joined in various geometric arrangements by free-rotation multi-connection joints. Tensioned cords, in the prototype high-strength fishing lines, run through the joints, surrounded by supporting nylon collars to reduce friction at the points where they contact. The cords provide enough elasticity and strength to pretension the joints but still facilitate movement.

At the joints the cords are wrapped around themselves to create simple knots. The knots allow the joint to resist compressive as well as tensile loads; even under compressive loads the cord is in tension as the ends of the rods try to push past each other.

Each rod has a load sensor connected to the actuator’s motor to allow it to respond to loads imposed upon the frame. This gives the user the option to change the frame’s form by pushing or pulling it by hand, and then locking it into that shape. It can also be manipulated by remote control. The load sensors give the frame a degree of structural autonomy – it can redistribute its structure to concentrate material at stress points – and they also act as failsafes to protect the frame’s mechanism.

Harkin says: “The joints are the focus area, they give complete freedom of movement via a very simple mechanism and the load is efficiently transferred at the intersection of the rods. With more than two joints meeting at the same point, it’s precise enough to keep almost precise concentricity with the rods’ axes. The rigidity comes from the tension in the cord, and the frame’s triangles give you the maximum amount of strength. It’s not perfect, but it works well enough to be a viable solution.

“With a larger demonstrator I want to see what wears out, to work on reliability and robustness.”