While chain is a good solution for pulling, it can’t be used to push the load – or can it?
The answer is yes thanks to the Framo Morat LinearChain Actuation System, available in the UK from R. A. Rodriguez. Here the company looks into the benefits and the suitable applications
In theatre engineering, push-pull actuation using chain is commonplace where the loads are exceptionally high. Now, however, Framo Morat has developed the concept to have much wider commercial appeal – providing stroke lengths up to 30m with a maximum push force of up to 35,000N with a single chain.
A special profile with interlocking fingers allows the chain to become a rigid thrust device for pushing a guided load, such as on a linear slide or a rail. LinearChain also rolls up into a magazine and is therefore particularly suited to applications calling for long strokes where space is at a premium. Furthermore, the device provides high positioning accuracy, constant stroke speed and shock-free motion with no elastic hysteresis under load.
However, its compact nature is one of the main selling points. Alternative methods for pushing a load include a piston rod, for example, but the design envelope needs to be twice the length of the stroke. Or, if the load is mounted on a carriage with driving wheels, a power pack and electrical or hydraulic services need to be accommodated too. Not only does this make the resultant system cumbersome and bulky, but it also prevents its use in harsh environments.
LinearChain can be unfurled through a gap measuring just 100mm square, and it can also be fed from a vertically-mounted magazine. As a result, substantial lengths of chain can be stored and turned through 90° on a sprocket to provide long stroke, linear motion. And, as it can be used in temperature extremes – from -50°C to +600°C – it has proven to be a solution for heat treatment furnaces. Annealed steel chains are available for such applications.
Although the maximum capacity of a single chain is 3.5 tonnes, loads in excess can be accommodated by simply adding more chains. LinearChain is also electrically driven, making it much more manageable and easy to control.
The design potential and application scope of LinearChain is huge, and it is increasingly being specified for scissor and other industrial lifts, as well as for platform positioning.
It has, for example, been selected by a company manufacturing lifting columns for installation in buildings for the lifting, lowering, turning, slewing and docking of heavy loads from one floor to another. Depending on the application, the lifting column is supplied as a rigid or slewing unit and in different heights up to 6m.
The travel direction of the chain is altered twice through 90°, allowing the column to be a free standing unit on the floor or mounted to the ceiling without the need for additional space to be allocated for the storage of the chain.
Another application is a new scissor lift destined for aerospace manufacturing and maintenance, where hydraulic rams were initially considered as a method of actuation. This is a common choice for arduous lifting but the size of the rams and the need for additional support equipment ruled them out for this compact design.
“By using the Framo LinearChain, the customer can achieve a much more streamlined and lightweight construction and is able to effect a straight life,” explained Paul French of R. A. Rodriguez. “An hydraulic ram by comparison would be a much bulkier and heavier mechanism in order to push the geometry of the scissor lift.”
In this instance, the device was specified as a stand-alone unit due to the high torque requirements of the application: 3700Nm. In most cases, R. A. Rodriguez supplies the LinearChain with the complementary Compacta slip-on geared motor which has a maximum torque of 1600Nm and is suitable for most push-pull applications.
The minimum space the LinearChain occupies is of particular importance in this application due to the very low platform start position required. This makes it easy for engineers to step on and off whilst carrying equipment.
French added: “Not only did the Framo LinearChain meet the design and performance needs of the application, it was also a cleaner solution and a much more cost effective method of actuation too.”
R. A. Rodriguez
T: 01462 670044