Patent Application
20110270437
The present invention relates to entertainment venues that have multiple mechanical loads being moved, such as lighting, scenery, curtains, etc., and specifically to a system for controlling movement of the loads.
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.
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.
Referring to
The communication link 26 is coupled to a machine controller 28 in each of the machines 18. The machine controller 28 is wired to the motor 20 of the corresponding machine 18 through a machine control link 30, which passes through a normally-open switching element 32.
The system controller 24 can be programmed in a variety of ways to achieve a software-based load management system. For example, the system controller 24 can be programmed such that select commands and movement commands can only be sent out to a limited number of machines 18 at any given time. In this way, the system provides a means for limiting the dynamic mechanical load that will be placed on the performance venue structure (e.g., that might be caused by simultaneous starting or stopping multiple machines 18).
A dead man circuit 34 is coupled between the control center 22 and the machines 18 to provide a hardware system for limiting the number of machines 18 that can be operated at any given time, thereby limiting the dynamic load created by the corresponding accessories. The illustrated dead man circuit 34 is hard-wired between the control center 22 and the machines 18, and includes no software for operation. In this regard, when the system controller 24 includes a programmed means for limiting the number of machines 18 that can be operated at any given time, the hardware system described below acts as a backup to the software system.
The portion of the dead man circuit 34 in the control center 22 includes a supply voltage 36, a dead man enable switch 38, and a dead man trip 40. The illustrated supply voltage 36 is a twenty-four volt source. The dead man enable switch 38 is normally open and can be manually closed by a user by pressing a dead man button 42. As with a typical dead man enable switch 38, the button 42 must be held by the user throughout the time that machines 18 are moving.
The closing of the dead man circuit 34 is sensed and communicated to the system controller 24 through a dead man status link 43. This information is used by the system controller 24 as an indication that the system is ready for machines 18 to move, and thus movement commands can be sent to the appropriate machines 18. In the illustrated embodiment, the system controller 24 is programmed with a slight delay (e.g., 100-200 mSecs) between the time it senses that the dead man circuit 34 is ready and the time it sends the movement commands. This delay provides sufficient time for the current in the dead man circuit 34 to stabilize, as described below in more detail.
The dead man trip 40 is a hardware device that will open the dead man circuit 34 if the current in the circuit exceeds a predetermined value. The dead man trip 40 includes a trip contact 44, a current measuring device 46, a comparator 48, a max current source 50, a hold unit 52, and a reset unit 54. The trip contact 44 is a normally closed switch that is coupled to the hold unit 52. The illustrated current measuring device 46 and shunt resistor (R-102) is a high side current measuring device that produces an output voltage corresponding with the current in the dead man circuit 34. The illustrated comparator 48 is an op-amp comparator that receives inputs from the current measuring device 46 and from the max current source 50. If the current in the dead man circuit 34 exceeds the current from the max current source 50, the output of the comparator 48 will cause the trip contact 44 to open. The hold unit 52 will maintain the trip contact 44 in the open position until it is manually reset by a user pressing a reset button 56 of the reset unit 54.
As noted in more detail below, in the illustrated embodiment, when a machine 18 is selected, it will draw 10 mA in the dead man circuit 34. If it is desired to limit the number of selected machines 18 to four, then the maximum current source 50 will be set between 40 mA and 50 mA (e.g., about 45 mA), which will not trip the comparator 48 when four machines 18 are selected (producing 40 mA current in the dead man circuit 34), but will trip the comparator 48 when five machines 18 are selected (producing 50 mA in the dead man circuit 34). In the illustrated embodiment, the max current source 50 can be adjusted depending on the structural integrity or strength of the building into which the system is being installed. In one embodiment, the max current source is a hardware jumper that has four levels, corresponding with the maximum selection of 2, 4, 6, or 8 machines.
As shown in
Each parallel loop 60 further includes a current sink 66 that draws a predetermined current. The current drawn by each current sink 66 represents the “load” of the corresponding machine 18 and related accessory. In the illustrated embodiment, each current sink 66 draws 10 mA, and thus each of the loads is approximated to be the same for purposes of the dead man circuit 34. It should be appreciated, however, that the size (i.e., current draw) of each current sink 66 could be designed to be proportional to the actual mechanical load of the corresponding machine 18 and accessory.
Each parallel loop 60 also passes through the corresponding switching element 32. The illustrated switching element 32 includes a relay 68 and a machine switch 70. The switching element 32 is designed such that the machine switch 70 is normally open, and is only closed when there is current passing though the relay 68. In one embodiment, the switching element 32 includes an opto-coupler 72 in order to electrically isolate the dead man circuit 34 from the machine control link 30.
It should be understood that the above-described components are described in relation to the illustrated embodiment, and their description in a particular orientation would not necessarily be required in order to practice the present invention. For example, while the machine controller 28, switching element 32, unit select switch 62, and current sink 66 are all described and illustrated as being within the confines of the machines 18, some of those components could be positioned outside the machines 18. Similarly, some of the components of the dead man circuit 34 that are illustrated as being positioned in the control center 22 could be positioned outside the control center 22 (e.g., in their own housing).
In operation, the above-described components function to limit the number of machines 18 operating any a given time. Prior to operation of a machine, the dead man enable switch 38 and all unit select switches are open, and thus there is no current flowing in the dead man circuit 34. In addition, the machine switches 70 are open, thus preventing the machine controller 28 from initiating operation of the corresponding machine 18.
Referring to
The user then must press 88 the dead man button 42, which closes the dead man enable switch 38. This allows current to flow through the dead man circuit 34. More specifically, current will flow through the parallel loop 60 in the selected machine 18, which will close the machine switch 70 corresponding with the selected machine 18.
After the dead man circuit 34 is closed, the system controller 24 waits 90 for about 100 mSecs for the current in the dead man circuit 34 to be filtered, stabilized, and analyzed. The wait period is chosen to be sufficient time for the dead man trip 40 to function prior to movement of the machine(s) 18. That is, the time delay allows the dead man trip 40 to determine whether too many machines 18 have been selected, which would result in tripping the dead man circuit 34 and preventing movement of any machines 18. In this regard, the overload management system of the present invention provides a proactive overload management that is hardware based.
During the wait time, the dead man trip 40 measures 92 the current in the dead man circuit 34 and compares 94 the measured current to a maximum current. At that point, a decision 96 is made whether or not the measured current exceeds the maximum current. If no, then the dead man circuit 34 remains closed, and the system controller 24 will send 98 a movement command to the machine controllers 28 after the above-referenced wait period. This will result in moving 100 the selected machine 18.
Alternatively, if the measured current is above the maximum current, then the dead man circuit 34 is opened 102 by opening the trip contact 44, and the machines 18 are stopped 104 or prevented from moving. In this situation, the trip contact 44 is held open by the hold unit 52, and the hold unit 52 can then be reset by the reset unit 54, as described above.
As noted above, the illustrated embodiment is designed to limit operation of no more than four machines 18 at once. As a result, if start commands are given for five machines 18, the resulting current in the dead man circuit 34 will be 50 mA, which will cause the dead man trip 40 to open the trip contact 44 to disable the dead man circuit 34. With no current flowing through the dead man circuit 34, the switching elements 32 in the machines 18 will revert to their normal states, causing all of the machine switches 70 to open. This cuts communication between the machine controllers 28 and the motors 20, thereby preventing operation of all machines 18.
When a start command is provided while some machines 18 are already moving, the same logic occurs. In this case, however, there is already current in the dead man circuit 34 (from the machines 18 that are already operating). Any additional machines 18 that are selected will then add to the current in the dead man circuit 34. If the total number of machines 18 operating plus the numbers of machines 18 selected for operation exceed the maximum allowable, then the dead man trip 40 will open the trip contact 44, and all machines 18 will be stopped, as described above.
The above-described system provides a means for limiting the number of machines 18 being operated at the same time. The system (i.e., the dead man circuit 34) is purely hardware, and thus is not reliant on proper software operation. It should be understood, however, that this system can be used as a back-up to a software system for limiting operation of the machines 18. That is, the software in the system controller 24 can be programmed such that it will not allow operation of more than the maximum number of machines 18 at the same time. If the software system operates properly, then the load management system of the dead man circuit 34 is not utilized. However, if there is a malfunction of the system software, the dead man circuit 34 will limit the number of machines 18 operating at the same time.
It is also noted that the present invention is capable of not only stopping the machines when too many have been actuated, but also proactively preventing the machines from starting in the first place. In other words, it can prevent the dynamic pulse that occurs when too many machines are started before the machines are started. This is in contrast to a system that has a 3-phase circuit breaker that will only trip after the too machine have started to move, and thus doesn't avoid the start-up pulse caused by too many machines.
Although the present invention has been described with reference to particular embodiments, it should be recognized that these embodiments are merely illustrative of the principles of the present invention. Those of ordinary skill in the art will appreciate that a dynamic load management system and/or method according to the present invention may be constructed and implemented in other ways and embodiments. In addition, where methods and steps described above indicate certain events occurring in a particular order, those of ordinary skill in the art having the benefit of this disclosure would recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain of the steps may be performed concurrently in a parallel process when possible, as well as performed sequentially as described above. Accordingly, the description herein should not be read as limiting the present invention, as other embodiments also fall within the scope of the present invention.
