Material or article handling – Self-loading or unloading vehicles – Having elevating load body
Patent
1985-11-04
1987-09-01
Spar, Robert J.
Material or article handling
Self-loading or unloading vehicles
Having elevating load body
187 25, 254 9C, 318139, 318376, 320 14, H02J 700, B60P 144
Patent
active
046906061
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to loaders and particularly to the type of mobile loader which incorporates a variable height platform used for loading and unloading freight in, for example, the cargo holds of aircraft.
Mobile loaders are essential equipment for the loading and unloading of cargo into and from the holds of aircraft.
Such loaders often employ two platforms. One platform, usually referred to as a bridge provides an interface with the sill of the cargo door and remains in a substantially constant position with respect to the aircraft. The second platform cycles up and down either taking cargo from the bridge or delivering cargo to the bridge.
Heretofore, the second platform has always been raised and lowered by means of hydraulic systems acting through appropriate mechanical linkages which ensure that the platform maintains a substantially horizontal attitude.
The loaders are frequently moved by diesel engines with all the attendant problems of noise, air pollution, fuel spillages, safety hazards and high maintenance cost etc.
In order to move away from diesel engines some designers have followed a conversion approach whereby substantially standard vehicles have been taken and converted to electric power by the installation of motors and batteries, etc. Usually, however, the hydraulic platform actuating system has been retained with hydraulic pumps driven by electric motors. The major problem with this approach is that the resulting loaders have low performance and low energy efficiency, especially with respect to load lifting performance.
It has been calculated that for a typical service on a Boeing 747 aircraft where the hold is unloaded on arrival and then loaded for departure that over 55% of the energy required from a loader's power systems are required in the raising and lowering of the loading platform. Nearly 30% of the remaining demand is taken up in driving the loader to and from and around the aircraft.
It is, therefore, considered to be a prerequisite that lifting efficiency is of paramount importance in mobile loaders.
Hydraulic systems are notably inefficient in terms of energy consumption, much energy being wasted in pumping fluids. In the case of mobile loaders in airports once energy has been expended in raising the loading platform it is all totally wasted during lowering of the platform. The platform is usually lowered by bleeding-off the hydraulic fluid through valves, usually into a reservoir for use again later in raising the platform. The energy efficiency of hydraulically operated systems is typically about 35%. A result of such low energy efficiency is that the overall performance of such loaders is relatively low. Their driving speed is low and endurance is relatively short.
By employing mechanical systems instead of hydraulics to raise the platform, the mobile loader of the present invention provides for recharging the batteries when the loading platform is being lowered by switching the drive motor into an electrical generator.
According to one aspect of the present invention a method of operating a loader comprises raising a load by mechanical lifting means, the mechanical means being driven by at least one electric motor means powered from battery means and then lowering a load, the descent being controlled by regenerative braking and wherein the at least one electric motor means is switched to generator means by control means and power from the generator means is used to at least partially recharge the battery means.
Preferably the mechanical lifting means includes re-circulating ball-screw jacks. The lifting platform may be a relatively conventional design wherein the platform is maintained in a substantially level attitude by a known scissor arrangement. The re-circulating ball-screw jacks may be connected to the platform via the nut of the screw such that as the screw is rotated the nut and platform are caused to be raised.
Preferably two re-circulating ball-screws may be used and may be driven by a common electric motor via a transmission.
During, for example,
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Hinds William R.
Ipeco Europe Limited
Millman Stuart J.
Spar Robert J.
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