Improving ergonomics with workstation cranes

Key concepts

• Ergonomic equipment must be properly applied to create a workplace where employees can comfortably and safely perform their duties

• Enclosed-track bridge cranes provide effortless movement of loads throughout the horizontal axis

• There are several factors to considering when selecting a workstation crane, including type, capacity, suspension/mounting, motorized or manual, and height.

• The demand for ergonomic equipment has grown significantly as more companies use it to effectively improve productivity, increase quality, and enhance safety. Most importantly, the ergonomic equipment must be properly applied in order to create a workplace where virtually any worker can comfortably and safely perform a given task.

  Manufacturers have responded to this need for ergonomic equipment with a series of innovative products that have made it even easier for users to lift and move loads in a work cell. There have been many new devices, such as high-speed hoists, vacuum lifters, balancers, and manipulators, introduced to the market in recent years.

  The equipment selection process is critical in determining how successful a project or solution becomes. When a user picks the appropriate lifting device and applies the proper crane system to cover the area, the ergonomic goals established for the project are achieved.

  There are several factors to consider when determining the most appropriate workstation crane installation: type, capacity, suspension/mounting, motorized/manual, bridge/boom, and height.

  Type

  Workstation bridge cranes (Fig. 1) cover rectangular areas, and provide effortless movement of loads anywhere in the work cell. Load position in the cell has no real impact on ease of movement when using bridge cranes.

  Workstation jib cranes provide circular coverage over the work area. The jibs move easily at the very end of the boom, but become more difficult to operate as the load approaches the pivot point. For this reason, workstation jibs should be positioned so that the rotation of the equipment happens while the load is on the outer 1/2—1/3 of the boom.

  Capacity

  Workstation bridge cranes are available in capacities of 150—4000 lb. Workstation jib cranes range in size from 100—2000 lb.

  The general rule when specifying capacities for manually operated workstation cranes is “less is more.” If the maximum weight handled is 1000 lb, then the crane should be configured for this amount and not more.

  With manually operated crane systems, the lighter the equipment the easier it is to move and position loads. If capacity is “over-bought,” the operator needs to handle extra dead weight of the bridge with each movement, which makes the crane harder to manipulate.

  Suspension/mounting

  Workstation bridge cranes are free standing (floor mounted) or ceiling mounted. Free-standing cranes are usually easier to install and relocate if the equipment needs to be moved to a different area, and are well suited for areas where an overhead building structure doesn’t exist or the support is inadequate to withstand the forces applied by the crane. Free-standing workstation crane systems require a reinforced concrete floor at least 6-in. thick.

  Fig. 1. This 1,000-lb capacity, ceiling-mounted aluminum bridge crane easily manuevers airplane parts throughout the work cell. Ceiling-mounted systems need a building with an adequate overhead structure from which to hang the crane. There is nothing attached on the floor of the work cell that would interfere with the handling operation or obstruct workflow.

  Workstation jib cranes are column mounted or free standing (floor mounted). Free-standing enclosed track jibs are used for applications where there is not an adequate column or structure to support the crane. Although some of these jibs require a foundation, many of the cranes can be installed on an existing reinforced, 6-in. concrete floor.

  Column-mounted jibs require a building support that can withstand the forces applied by the crane. This type costs significantly less than free-standing workstation versions and doesn’t interfere with or obstruct movements on the work floor.

  When applying workstation jibs, the column-mounted style should be the choice whenever there is an adequate support available to mount the crane.

  Fig. 2. Jib cranes provide 360-deg coverage of the work area. They move more easily near the end of the boom; therefore, the load should be located away form the pivot point to maximize operational efficiency.

  Motorized or manual operation

  The decision of manual or motor operation depends on the weight, movement, and size of the load manipulated. If the crane is easy to move, operators prefer manually operated equipment because it allows them to work at their own pace (often faster) and provides more precise positioning of loads. But if the operator does not have continuous control of the load throughout the operation — over a vat, pit, or other inaccessible area, for example — the crane should be motorized.

  Most applications with loads of 4000 lb or less are safely maneuvered with a manual workstation bridge crane. Applications with loads greater than 4000 lb are often motorized, because capacities of this size are usually too difficult to maneuver and control manually.

  Bridge/boom length

  It is important to keep bridge and boom lengths to a minimum. The less dead weight an operator has to move, the better.

  Short bridge/boom lengths are preferred for higher-cycle production areas. Longer bridges/booms are acceptable for lower-production cycle applications.

  Height

  Bridge heights (trolley saddle) and boom heights should be kept as low as possible. A trolley saddle height less than 14 ft is desirable because it is easier to control and position the load.

  Edited by Ron Holzhauer, Managing Editor.

  Recent improvements

  Enclosed-track workstation bridge cranes provide effortless movement of loads in a work cell throughout the horizontal and vertical axes. There have been many recent improvements in this technology, including:

  Introduction of long spanning rail systems that provide larger coverage areas

  Aluminum rails that are lighter in weight and easier to move than previous steel tracks

  Synthetic wheel technology that lasts longer and rolls easier than previous steel wheels.

  Workstation cranes solve handling problems

  Autrans, an automotive manufacturer in Ingersoll, Ontario, Canada, needed to change its overhead material handling operations when the plant converted from a warehouse to a manufacturing facility. They chose free-standing bridge crane systems to serve their engine/transmission assembly lines because the building’s structure originally designed for warehousing could not support ceiling-mounted equipment.

  The new system has three bridges on a single runway 86-ft long. All bridges are 20-ft wide; two are 1000-lb capacity and the other is 500-lb capacity. Each bridge serves a work area approximately 28-ft long.

  In the first work cell, subcomponents for engines and transmissions are brought for assembly in palletized loads via lift trucks. The first bridge, with the 500-lb capacity, goes into action at the start of production. The operator utilizes the crane to pick up an engine from the pallets at the side of the work cell, and with the help of the electric chain hoist, moves the load and places it on a subassembly stand where parts are added by an operator using bridge two. The engine assembly is transferred to a fixture for mating with the transmission.

  The system is easy to move and position, and requires minimal training. The enclosed-track design of the bridge cranes virtually eliminates dust and dirt from the rolling surface, which reduces wear on the wheels of the trolley and end trucks. Their trussed support allows for long spans, which means fewer columns and less interference at the floor level.

  Transmissions are introduced to the process by a lateral feed conveyor, and carried by bridge three (1000-lb capacity) to the mating pallet that holds the engine. The transmission is joined with the engine housing and bolted together. The entire assembly is transferred to a jig on the main conveyorized assembly line where it passes through nine workstations for operations involving various tools. It is during this process that accessories, such as power steering pumps or an air conditioning compressor, are added. The assembly time is approximately 21/4 min/station.

  When the completed unit arrives at the end of the production, it is picked up by another 1000-lb bridge crane. The unit is then transferred to a shipping pallet on an in-floor roller conveyor. The pallet has a built-in fork enclosure to facilitate transferring the units to a delivery vehicle by a lift truck.

  Autrans has found that with the ease of movement of a workstation crane, employees exert little force to move material around their work cell. Consequently, the enclosed-track workstation cranes effectively eliminate many of the material handling injuries in the workplace, while reducing fatigue.

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