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Travel Height
The difference in elevation between the top surface of the carriage or carrier at the bottom most level and the top surface of the carrier or carriage at the uppermost level; regardless of whether the unit is pit or surface mounted.
Floor-to-Floor Distance
The distance from the top of one finished floor level to the top of the next finished floor level.
Capacity (Weight, Size and Type of load)
Capacity not only refers to the weight of the load but also the physical size and configuration of the load. Types of loads are typically: individual boxes and items, palletized loads, drums, pushcarts, and trucks, etc. The platform should be sized to handle the largest loads with adequate clearances for handling operations. The capacity should take in consideration the weight of the equipment used for loading and unloading operations in addition to the weight of the heaviest load. If the loading and unloading process has the potential for intended or unintended imposition of large horizontal forces, this must be taken into account during design.
Load Pattern
The load pattern of the loads for loading and unloading will determine which style of VRC configuration can be used. There are 3 basic load traffic patterns. The most common is a “Z” pattern where the load is placed on one side of the platform at one level and removed from the opposite side at another level. The second traffic pattern is the 90-degree pattern where the load is placed on one side of the platform at one level and unloaded to the right or left (90 degrees) at the another level. The last is the “C” pattern where the load is placed on and removed from the same side of the platform at each level. It is also possible to have a combination of load patterns on multiple level or special applications. In some very special applications, it may require 3-way or 4-way loading and unloading but these are rare and require special designed platforms.
Loading and Unloading Methods
Consideration of the loading and unloading methods must be given when specifying a VRC as it may affect the design of the platform and the capacity of the unit. For instance, loading with a hand operated pallet jack may not require the same type of platform construction and unit capacity as loading with a powered pallet jack. Also, loading with a powered fork truck may not be allowed at either level depending on the VRC design specified, unless the specification explicitly calls for fork truck roll-over capacity and it is designated at which elevation or level a fork lift truck will be used. Note: This is true only in those applications where the fork truck must enter a platform in order to place the load. If the fork truck merely places the load on the platform without traveling onto the platform surface, then a standard VRC should handle the application, in which case restraints, curbs or a barrier should be provided to prevent fork truck entry onto the platform. Consideration should also be given to loads that may place a concentrated load on the platform and/or may not be on the platform’s load center. Most VRC manufacturers assume uniform loading over the entire platform surface. Wheeled carts or trucks and pallet jacks are prime examples of this type of loading. When a VRC is used in an automated system with powered conveyor mounted on the platform, the reactionary forces of the load starting and stopping should be anticipated and proper supports incorporated into the installation design. It should also be noted that turntables and pushers should be given special consideration because of the abnormal forces they generate. When using hydraulically actuated VRCs in automated systems, it may not be advisable to use an upper level as the “Home Position” unless special consideration is given to the hydraulic circuitry and/or automatic re-leveling control circuit design. Mechanical type VRCs are not subject to down drift as with hydraulic VRCs and therefore, should be the first consideration for automated system applications.
Platform Guarding and Accessories
VRC platforms can be manufactured in an infinite number of configurations. The load to be transported should be considered when determining the style, construction, height and type of guarding and accessories that are selected and specified. The minimum guarding requirement to meet the safety standard is nominal 42” high handrails with mid-rail and 4” high kick-plate on the non-operating sides of the platform and a snap chain that is a minimum of 39” high at its lowest point, mounted across the loading or operating side(s). Depending on the type of load being conveyed, fixed panels may be substituted for handrails on the non-operating sides of the platform. Fixed panels constructed of solid sheet or expanded metal panels may be preferred. Typically, these are minimum 48” high or higher depending on the type of loads. Drop bars or other devices mounted to the platform that lower to prevent rolling loads from moving off the platform during operation may be required.
Gates and enclosures are required in accordance with ASME/ANSI B20.1. All gates, whether vertical acting, horizontal sliding, or swing gates, must be equipped with an interlock.
The safety of a gravity or powered roller conveyor used in conjunction with VRCs must also be considered. Many automated systems, using a powered conveyor for loading/unloading, have different guarding requirements. Consult your VRC supplier.
Electrical Considerations and Usage
Operating conditions such as outdoor, wash down area, airborne dust, oil mist, etc. must be considered. Area activities such as a large volume of fork truck or people traffic may require special protection considerations and/or key lock type controls for use only by authorized personnel.
Operational Considerations
The controls may be of a constant pressure type where the operator must hold the operating button until the lifting or lowering cycle has been completed. They may also be momentary contact call/send type, which only requires the operator to press the directional button momentarily, allowing the VRC to automatically travel to the level the operator has chosen and stop at that floor level by means of an electrical switch.
When loading a VRC with a fork truck, a ceiling mounted pull cord type switch may be desirable to activate the VRC and/or powered access gate.
In automated systems the control system may be operated by a computer.
Mechanically Driven
This is the unit of choice for environmentally conscious and higher duty cycle considerations. These units are best used for two or more levels of travel where intermediate stops are required, automated system applications, and high speed or high cycle projects. This system utilizes an electric brake motor with a gear reducer.
The carriage is typically raised or lowered by means of heavy-duty cables or chain. Travel is controlled with an electrical limit switch or similar device at each level. Stopping accuracy is normally good in loaded and unloaded conditions.
Sizing a Power Unit
A VRC unit should be sized to properly handle its rated working capacity, the lifting speed, and its duty cycle with an additional safety factor. Include weight of platform-mounted accessories when specifying the rated capacity.
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