The assignee for this patent, patent number 8710704, is
Reporters obtained the following quote from the background information supplied by the inventors: "Performance venues such as theaters, arenas, concert halls, auditoriums, convention centers, television studios, and the like can employ battens or trusses to raise and lower lighting, scenery, set-pieces, displays, draperies, and other items. Lift assemblies, or hoists, are typically used to raise and lower battens or trusses and attached loads. The lift assemblies are commonly connected directly to the support structure of a building, for example, to overhead beams. In some lift systems, multiple lift assemblies, or machines, can be employed for moving heavy loads, and can be connected to the same support structure.
"Variable numbers of lift machines can be selected to operate for moving particular loads, such as a stage curtain and scenery. In a situation in which the stage curtain and scenery need to be raised at the same time, two lift machines can be selected to operate simultaneously. When multiple lift assembly machines are started, stopped, sped up, or slowed down at the same time, the moving mass and inertia of the machines and attached loads can place a large dynamic load on the support structure. As used herein, 'dynamic load' refers to a dynamic mechanical load created by the acceleration or deceleration of a mass. For example, dynamic load on a building structure can be created by the force exerted by the inertia of starting, stopping, speeding up, or slowing down one or more accessories connected to the structure.
"In locations where lift assemblies are installed, for example, to the 'flytower' above a stage, the building support structure is often designed to handle the dynamic load of only a few lift machines starting and/or stopping at the same time. If too many lift machines are started and/or stopped at the same time, the associated dynamic load can cause damage to the support structure. Accordingly, the number of machines that are started or stopped at the same time may need to be limited in order to limit the dynamic load created.
"Lift assembly systems that employ multiple lift machines often include a primary safety mechanism to prevent excessive dynamic loading on the support structure when the machines are started or stopped. Generally, such safety mechanisms are controlled through software. One risk of a software-based safety mechanism is that the software can malfunction or fail due to loss of power, inherent or acquired bugs, misuse by an operator, or other reasons. Thus, it is often desirable to have a dynamic load safety backup system that prevents the start of too many machines.
"Some conventional multi-machine lift systems utilize an operator-activated safety backup mechanism to avoid overloading the building support structure to which a system is connected when multiple machines are started, stopped, or speed changed at the same time. For example, when signaled that an excessive dynamic load is being exerted by start-up of multiple machines, an operator can hit an 'emergency stop' button to shut off power and stop operation of the machines. A significant disadvantage of such an operator-activated safety mechanism is that simultaneously stopping operation of multiple machines can suddenly release the excessive dynamic load in one direction and thereby create an excessive dynamic load on the support structure in the opposite direction. Another disadvantage is that such an operator-activated safety backup mechanism is engaged 'after the fact,' following initiation of an excessive dynamic load, and is dependent upon an operator monitoring for an excessive load.
"Some conventional multi-machine lift systems utilize a software-based program as a safety backup mechanism to avoid an excessive dynamic load. Such software allows only a limited number of machines to be selected for movement at one time. One disadvantage of a software-based safety mechanism is that the software can malfunction or fail due to bugs in the software, or when used in applications that exceed software parameters. Another disadvantage of such a software-based safety mechanism is that certifying such systems for safety according to regulatory and/or industry standards can be complicated (if not impossible), time-consuming, and costly."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "The present invention provides a dynamic load management system that is particularly suited for use in managing the loads present in a performance venue, such as a theatre, auditorium, stage, television set, convention center, or any other similar forum. More specifically, the present invention is designed to use a dead man circuit as a means for determining the actual or anticipated dynamic load produced by moving loads, such as lighting, scenery, set-pieces, displays, draperies, and other items, and then disabling the system by opening the dead man circuit when too many machines are moved or selected to be moved. The system can be a primary dynamic load management system, or it can be a secondary or fallback system.
"In one embodiment the invention is found in a performance venue comprising a plurality of machines (e.g., hoists) designed to move loads, a control center, a communication link coupling the control center to the machines, a machine switch (e.g., in each machine) coupled to the communication link and movable between an open position and a closed position, and a dead man circuit. The dead man circuit comprises a dead man enable switch movable between an open position and a closed position, a switching element (e.g., in each machine) coupled to the machine switch and operable to move the machine switch to the closed position, and a dead man trip that will open the dead man circuit when current in the dead man circuit is outside a desired range (e.g., when the actual current exceeds a max current). In a preferred embodiment, the dead man trip includes a current measuring device, a comparator coupled to the current measuring device, a trip contact, and a hold unit designed to hold the trip contact open when it is tripped.
"Preferably, the control center includes a system controller coupled to the communication link and operable to provide a machine select command to each of the machines. In this design, each machine can include a machine controller coupled to the communication link and operable to receive the machine select command. The dead man circuit can further include a unit select switch corresponding with each machine, and wherein each machine controller is operable to move a corresponding unit select switch to a closed position. The dead man circuit preferably includes a plurality of parallel branches corresponding with the plurality of machines, each branch including a unit select switch, a switching element, and a current sink. In its most-preferred embodiment, the dead man circuit is pure hardware and is free of software components.
"The present invention can also be found in a method of controlling movement of loads in a performance venue having a plurality machines for moving the loads. In its basic form, the method comprises selecting at least one of the machines for movement, closing a dead man circuit (e.g., by pressing a dead man button), and opening the dead man circuit if the current in the dead man circuit falls outside a predetermined range. Preferably, the dead man circuit includes a trip contact, and the step of the dead man circuit includes measuring the current in the dead man circuit, comparing the measured current to a maximum current, and opening the trip contact if the measured current exceeds the maximum current.
"Features of a dynamic load management system and/or method may be accomplished singularly, or in combination, in one or more of the embodiments of the present invention. As will be realized by those of skill in the art, many different embodiments of a dynamic load management system and/or method are possible. Additional uses, advantages, and features of aspects of the present invention are set forth in the illustrative embodiments discussed in the detailed description herein and will become more apparent to those skilled in the art upon examination of the following."
For more information, see this patent: Lichter, Michael; Nolan,
Keywords for this news article include: Software,
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