The great benefit of using chain to move a load is that it can be stored compactly, a clear benefit in systems design.  But whilst it is a good choice for pulling, chain can’t be used to push the load.  Or can it?  The answer is yes thanks to the Framo Morat LinearChain Actuation System.  Introduced to the UK by R. A. Rodriguez two years ago this innovative product is proving to be the perfect choice for a wide variety of applications across industry.

Push-pull actuation using chain is commonplace in theatre engineering where the loads are exceptionally high and until recently this reciprocal chain movement remained unique to this sector.  Framo Morat has now developed the concept to have much wide commercial appeal, providing stroke lengths up to 30m with a maximum push force of up to 35,000 N 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.  The LinearChain rolls up into a magazine and is therefore particularly suited to applications calling for long strokes where space is at a premium.  The device provides high positioning accuracy, constant stroke speed and shock-free motion with no elastic hysteresis under load. 

The compact nature of this solution is proving to be one of its main selling points.  And it’s easy to see why, when the LinearChain is compared to alternative methods for pushing a load. If a piston rod is used for example, 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.  It can also be fed from a vertically-mounted magazine.  In this way substantial lengths of chain can be stored and turned through 90? on a sprocket to provide long stroke, linear motion. 

It can also be used in temperature extremes, from -50?C to +600?C and in this regard has proven to be a good 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.  And another important factor is that LinearChain is electrically driven making it much more manageable and easy to control.

The design potential and application scope of LinearChain is huge but one sector in particular is benefiting from this technology.  LinearChain is increasingly being specified for scissor and other industrial lifts and also for platform positioning. 

For example, LinearChain was 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?.  This allows 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.

A new scissor lift destined for aerospace manufacturing and maintenance is another new LinearChain application for which 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.  “A 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 Framo LinearChain 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 required, very low platform start position.  This makes it easy to engineers to step on and off whilst carrying equipment.

Paul French concludes: “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.”