In engineering, iso-elastic refers to a system of

elastic Elastic is a word often used to describe or identify certain types of elastomer, elastic used in garments or stretchable fabrics. Elastic may also refer to: Alternative name * Rubber band, ring-shaped band of rubber used to hold objects togeth ...

and

tensile In physics, tension is described as the pulling force transmitted axially by the means of a string, a rope, chain, or similar object, or by each end of a rod, truss member, or similar three-dimensional object; tension might also be described as t ...

parts (springs and pulleys) which are arranged in a configuration which isolates physical motion at one end in order to minimize or prevent similar motion from occurring at the other end. This type of device must be able to maintain angular direction and load-bearing over a large range of motion. The most prominent use of an iso-elastic system is in the supporting armature of a Steadicam, used to isolate a film or video camera from the operator's movements. Steadicam arms all work in a fashion similar to a spring lamp since each arm has two sections (similar to and labelled like a human arm); both the upper and fore-arm sections consist of a

parallelogram In Euclidean geometry, a parallelogram is a simple (non- self-intersecting) quadrilateral with two pairs of parallel sides. The opposite or facing sides of a parallelogram are of equal length and the opposite angles of a parallelogram are of equa ...

with a diagonal iso-elastic cable-pulley-spring system. The iso-elastic system is tensioned to counteract the weight of the camera and steadicam sled. This tensioning allows the camera and operator to move vertically and independently of each other. For example, as the operator runs, the bouncing of his body is absorbed by the springs, keeping the camera steady. The arm also has unsprung

hinge A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation: all other ...

s at both ends of each arm allowing it to bend in the horizontal plane (just like your elbow, not like a spring lamp). To understand how an iso-elastic system works, we must first understand how springs work. The tension (elastic force) in a spring is proportional to its extension according to

Hooke's law In physics, Hooke's law is an empirical law which states that the force () needed to extend or compress a spring (device), spring by some distance () Proportionality (mathematics)#Direct_proportionality, scales linearly with respect to that ...

. This means that if a weight is hung on a spring it will oscillate with simple harmonic motion about its balance point; when the weight is above the balance point the spring's tension is reduced so the weight falls due to gravity, and when the weight is below the balance point the spring's tension will pull it back upwards. If a simple spring system were used in a steadicam, then as the operator moved vertically, the camera would be subject to simple harmonic motion, and bounce up and down. To counteract this tendency, an iso-elastic system is employed. The springs used are large, stiff springs with a high modulus of elasticity, and they are highly tensioned. A compound pulley system is then used so that the large force exerted by the spring can be divided by a factor of five, for example, so the cable exiting the pulley system will have only moderate tension. Most importantly, however, when the cable is drawn in or out the extension of the spring changes by only a fifth of that distance, so that the tension force of the spring will not change much. The result is that the spring-pulley system can produce a fairly constant tension in the cable over a large range of movement. The almost constant force exerted by an iso-elastic system is employed in the armature of a steadicam, to counteract the constant force of

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

on the camera's and mount's

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...

. The result is that the

weight In science and engineering, the weight of an object is the force acting on the object due to gravity. Some standard textbooks define weight as a Euclidean vector, vector quantity, the gravitational force acting on the object. Others define weigh ...

of the camera is almost exactly balanced by the tension force throughout the entire range of vertical movement, so even when the operator jumps vertically, the camera will retain its vertical position due to inertia, but remain balanced, just with the armature at a different angle. As a result, the camera doesn't bounce up to the 'balanced' position after a move, for example when the operator steps up onto a curb from the road. This allows the camera to be more isolated and independent of the operator's moves. The operator can of course deliberately move the camera up or down, if desired. In reality however camera operators find it preferable for the arm to not be perfectly iso-elastic so that the camera will naturally rise to a comfortable operating height; the springs will be tensioned so this only happens very slowly and without bouncing so as to maintain the smoothness of the camera's motion."Adustable, iso-elastic support apparatus US 5435515 A.

References

{{DEFAULTSORT:Iso-Elastic Engineering concepts Cinematography

See also

References