While grouping work stations closely together minimises material movement and conserves floor space, it means production flow needs to follow increasingly complex circular and oval paths. HepcoMotion takes a look at the options available for this
Although frequently chosen, a belt conveyor system can only move payloads in straight lines. If a multicurve path is needed, it is achieved by mounting multiple straight conveyors at a series of offset angles or by using belts with interlinked pivoting segments – luggage conveyors at airports provide a good example.
A roller conveyor is slightly more flexible as it can be mounted in a frame configured to follow a specified curvilinear path. It can be powered by motors coupled to the rollers directly or by intermediate drive belts; or it can be un-powered with the payload moved by gravity or by hand.
Overhead trolley systems can easily follow multicurve paths on tracks mounted high above the floor to which are attached wheeled carriages. The payload on this type of conveyor is suspended from the carriages and it can be moved by hand or pulled by motor-driven chains along the track.
Slewing rings or turntable bearings are often incorporated into the conveyor handling systems to provide movement through 360°. These are large machine bearings that are capable of handling high load capacities and are often specified with gear racks machined into their races for direct driving.
Accuracy and precision
A vee-bearing based ring and track system, however, can offer both positioning accuracy and precision, a benefit when the load is fragile or must be held rigidly and accurately positioned on the process line. One reason for this is that the vee bearings are designed to be firmly pre-loaded against the slide, ensuring the carriage’s stability along its path of travel.
The same level of positioning accuracy isn’t generally possible with belt and roller conveyors where the load is primarily kept in place by gravity and often constrained by side guide rails. The load is also subject to continuous vibration and this may cause it to skew, become damaged or block the flow.
Any conveyor system that relies on gravity for constraining the payload limits flexibility of movement, in particular the possibility of moving it vertically. Furthermore, it must carry the load directly over its moving elements and can’t transport it up or down steep inclines.
Overhead trolley system carriages only have sufficient constraint to prevent the load falling off the track and generally use non-rigid linkages, such as chains or hooks, to carry it. This too is a hazard as it allows the load to swing freely. For the sake of stability, such systems must have their load directly hanging from their carriages and cannot move up or down steep sections as the load can’t be allowed to make contact with the track or load on adjacent carriages.
With a vee-bearing based ring and track system, however, the load can be securely mounted at any position relative to the carriage. It can also be transported in any direction, regardless of gravity, as the carriage wheels are firmly held against the slides and only permit movement along the designated path.
Such systems can also require less space, support structure and maintenance, and its carriages can carry wider loads, allowing a smaller footprint.
An overhead trolley system can carry a relatively wide payload but requires a sizeable and sturdy support structure because its track systems have to be elevated high enough for their under-hung payload to be accessible and clear of any ground level obstacles. These structures can make it complicated and expensive to assemble and re-configure, and they can be difficult to keep clean.
For handling applications that require a lot of circular motion, turntable bearings are far more suitable than conveyors. They are more compact, weigh less and are available as fully assembled units that can be integrated quickly into a process line. They also offer accuracy and smoothness and, like a vee-bearing based system, can have the payload mounted to them. Nevertheless they do have some disadvantages.
Although ease of assembly is common to both a vee bearing based rotary system and a turntable bearing, the former is easier to service as its components are interchangeable. The precise assembly and machining required by a turntable bearing means it is generally fully assembled in the factory. So, if a component fails, the entire ring has to be replaced; and as it is also often the mounting structure for application components, replacement of the bearing can also involve reassembling all the ancillary components too.
Only damaged components need to be replaced on a vee bearing based rotary system and, thanks to their common fit design, individual components can be used in any compatible system. It is often possible to exchange components without the need for disassembly.
While turntable bearings offer better rigidity than conveyor systems, they are generally not pre-loaded. Although a common feature of smaller machine bearings, larger components are harder to machine precisely and their form and fit are more affected by external factors.
Small manufacturing flaws, component deformation due to external loads, uneven mounted surfaces or non-uniform thermal expansion are much more likely to have an impact on preload. Any preload change can result in internal component clearance which reduces system rigidity, or high interference, which makes rotation more difficult and can damage components.
In addition, a turntable bearing’s preload level depends on internal component dimensions and can’t be adjusted after assembly.
Vee-bearing based ring slides can have a significant size advantage over turntable bearings in applications requiring less than 360° of travel. Additionally, these bearings must be fully circular to provide a complete travel circuit for their rolling elements, even if the application requires far less than the full 360°.
Only the ring slide segment arc length needs to be long enough to support all the vee bearings, which can be as few as three, throughout the full arc of travel.
As a result of the features mentioned above, vee-based ring and track systems can greatly improve payload transportation, simplify handling and boost efficiency. Furthermore, they offer design flexibility and are easily adapted.
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