Patent Publication Number: US-2023148011-A1

Title: Dock area control system

Description:
This application is being filed on Mar. 19, 2021, as a PCT International Patent application and claims the benefit of and priority to U.S. Provisional patent application Ser. No. 62/993,035, filed Mar. 22, 2020, the entire disclosure of which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Proximity Detection Systems and Collision Avoidance systems (PDSC) are being used worldwide for minimizing collisions between vehicles, to prevent hitting and/or crushing personnel, and to prevent costly hardware and facility damage. The earliest successful solutions were developed for use in underground mining applications, using pulsed low frequency magnetic fields. Pulsed low frequency magnetic fields have been successfully modified and augmented with new devices to provide proximity detection and collision avoidance for numerous industries. Solutions have been developed for operation of vehicles in open areas, open storage in warehouses, and a variety of manufacturing and materials handling applications, especially for using fork lifts. Very narrow aisles (VNAs) in warehouses that utilize very tall metal rack systems posed extra challenges which were solved by adding the use of vector components of magnetic fields and/or compasses. See the Frederick patents, discussed below. This technology has been proven effective for providing Proximity Detection Systems (PDS) and Collision Avoidance Systems (CAS) (PDS/CAS or PDSC) in many industrial environments. 
     The high reliability and precision of these pulsed low frequency magnetic field systems has led to a variety of system configurations and devices that protect personnel (pedestrians, vehicle operators, and other people, whether performing work or not, are generically referred to as “workers”), prevent collisions between vehicles and/or machines, and prevent collisions with facility items. Examples of these devices are disclosed in U.S. Pat. No. 7,420,471 (the &#39;471 patent), U.S. Pat. No. 8,169,335 (the &#39;335 patent), U.S. Pat. No. 8,552,882 (the &#39;882 patent) U.S. Pat. No. 8,232,888 (the &#39;888 patent), U.S. Pat. No. 8,446,277 (the &#39;277 patent), U.S. Pat. No. 8,847,780 (the &#39;780 patent), U.S. Pat. No. 8,710,979 (the &#39;979 patent), U.S. Pat. No. 8,810,390 (the &#39;390 patent), U.S. Pat. No. 9,081,046 (the &#39;046 patent), U.S. Pat. No. 9,280,885 (the &#39;885 patent), U.S. Pat. No. 9,822,927 (the &#39;927 patent), and U.S. patent publication 2018/0128932 (the &#39;932 publication), which patents and publications are herein referred to collectively as the “Frederick patents,” the disclosures of which are incorporated herein by reference in their entireties. Reference earlier Frederick patents for details on how the PDSCs and PADs function. The Frederick patents disclose the details about the construction and application of a successful PDSC system that has the necessary capabilities and characteristics for the current disclosure to be most useful. The following descriptions do not repeat the details of a PDSC already disclosed in the Frederick patents, for example, the general PING and ECHO response architecture, and the Warning zone and Danger zone alarms, protocols and configurations, but describe the current disclosure with the assumption that the reader will be acquainted with those PDSC ideas and inventions. 
     In addition to using proximity detection systems, facilities are frequently designed to try to provide added physical separation between pedestrians and vehicles, as much as possible, and to slower vehicle speeds. Enhanced separation of personnel from moving vehicles by use of mechanical barriers, by better training, and by use of magnetic field devices, such as mechanized area controllers, has reduced the number of some types of accidents. However, in some instances, these approaches have resulted in reduced production. And, there are numerous situations that necessitate both vehicles, such as fork trucks, and pedestrians to work in the same area. The fact that most fork trucks are driven by an operator illustrates that operators and trucks must sometimes be in the same area. In some instances, there is a mix of automatically-guided vehicles (AGVs), human-operated fork trucks, and pedestrians. One such example would be a large distribution center which includes roadways and docking portals. 
     Modern distribution centers create additional challenges for protecting pedestrians, collisions between fork trucks, and collisions with automatically guided vehicles. A typical distribution center has dozens or even hundreds of docking portals at which trailers are loaded or unloaded with products and materials. In the majority of the larger installations, loading or unloading of trailers is accomplished by use of low-profile fork trucks that drive from the dock into the parked trailers. Products are transported from storage areas, usually along roadways within the distribution center, until they reach the trailer that is to be loaded, such as trailers  115 ,  116 ,  117  and  118 , as depicted in  FIG.  1   . Sometimes, products are removed from a trailer  115 ,  116 ,  117 ,  118  and transported to storage. In some instances, products are transported directly from one trailer  115 ,  116 ,  117 ,  118  to another trailer or to a conveyor.  FIG.  1    illustrates the typical relationship between a roadway  50  and the portals  111 ,  112 ,  113 ,  114  through which trailers are being serviced by fork trucks at a loading dock  100 . 
     Although there are many configurations of distribution centers that are handling a wide variety of products and materials, a typical operation can be viewed as being in phases. Products arrive, in a first phase, on trailers or train cars and are removed by low-profile fork trucks and are taken to a temporary open storage. From there other fork trucks, such as reach trucks, transport the items or pallets of items and place them in large metal rack systems. Some products are not stored in metal racks but are stacked in open areas. Other fork trucks such as order picker trucks elevate workers as required to retrieve specific items, which are then moved to areas where they are packaged for delivery. From there they are organized for loading onto trailers or short-haul trucks. Finally, in a last phase, low-profile fork trucks carry the deliverable products, often on pallets, to staging areas or for loading into trailers. The first and last phases require low-profile trucks that enter portal areas and enter into the trailers or trucks. In many cases small fork lifts of the type that are operated by an operator who is in the standing posture, are preferred. A wide range of situations occur at loading docks that are dangerous and/or result in costly accidents. This disclosure introduces new devices and novel methods of advancing the capabilities of PDSC to save lives, reduce injuries, and to reduce costly accidents. Some materials handling tasks are now being performed by robotic vehicles, which can add to the complexity of the operations and can increase the chance of a costly collision. The current disclosure is applicable to robotic vehicles but typically, the PDSCs must be designed into the robotic vehicle by the original equipment manufacturer (OEM). 
     The number of pedestrians on loading docks varies with the design and function of the facility. Usually, there are policies that minimize the number of pedestrians in the busy area where fork trucks are arriving and departing from the portal areas. However, there are some specific jobs that require pedestrians to enter the portal areas near the trailers and/or to enter the trailers. Workers on foot may have to remove trash that falls from products or carriers, check markings and labels, provide inspections when there are problems or unexpected changes, coordinate movement of trailers between portals, lock the trailer onto the dock, inspect damage to trailers or products due to contact by truck forks, repair or service equipment, maintain records, etc. Truck operators must sometimes temporarily leave their truck for a few moments, on foot. If significant numbers of pedestrians are in a dock area, there may be a significant number of opportunities for being hit or crushed. If pedestrians are only rarely working in the dock area, fewer chances exist for accidents. Yet, when pedestrians are not frequently present, truck operators tend to be less prepared to quickly recognize danger to pedestrians or to respond rapidly. 
     It is sometimes necessary for a worker to be in a location where fork trucks may travel. PDSC systems can warn pedestrians and truck operators when they are dangerously close. Some systems like those disclosed in Frederick patents help to prevent both pedestrian and vehicles from being in the same area at the same time. Loading docks present situations that need smart systems, with much capability, but that are not costly to manufacture and install. The current disclosure is a Docking Area Controller (DAC) that includes a DAC Electronics Module (DEM) that satisfies these needs and others as well. As more robotic vehicles are added to distribution centers, new challenges result, including making sure that man operated trucks do not run over costly robotic vehicles and making sure that the robotic vehicles do not run over pedestrians. An added reason for growing complexity is that pedestrians may be required, from time to time, to resolve or correct situations that robotic vehicles have caused, which will also require pedestrians to be in the work area. 
     Thousands of accident reports each year reveal the many ways that a pedestrian can be hit or crushed by a fork truck or by the products that fork trucks are transporting. A simple, obvious danger is illustrated in  FIG.  1   . A pedestrian  101  is hidden from view by product  102 . The pedestrian  101  does not see the oncoming fork truck  103  and the operator of truck  103  does not see the pedestrian  101 . There are video-documented cases where a pedestrian  101  crosses in front of a fork truck  103  and the driver cannot see the pedestrian and runs them over. In such cases, the pedestrian  101  steps into the path of fork truck  103  and there is not enough time for the operator of the fork truck  103  to respond. Automatically Guided Vehicles are sometimes a concern because they may make very little noise and also because they may not be fully prepared to avoid a fork truck. 
     Fortunately, some types of accidents have been almost eliminated in facilities where PDSC systems have been implemented, particularly those that use pulsed low frequency magnetic fields. Pulsed low frequency magnetic fields pass through objects and also are shaped so that they pass around objects. Pulsed low frequency magnetic fields are also stable and precise. By using this kind of technology, a pedestrian  101  is warned by the personal alarm device they are carrying and the operator is also warned by the PDSC  107  installed on the fork truck  103 . Numerous Frederick patents provide explanations and illustrations that show how PDSC capability improves safety for many situations. There remains work to be done for other unsafe situations because there continues to be many harmful and costly fork truck accidents. 
     A potentially dangerous example that is more closely related to a primary objective of the current disclosure is also depicted in  FIG.  1   . As shown, a pedestrian  119  is working on the loading dock  100 . Fork truck  105  is approaching portal  112  to service trailer  116 . Pedestrian  119  is in the path of the truck  105 . Pedestrian  119  might be in that portal area  112  in order to perform work, passing through portal area  112 , or entering into or exiting from trailer  116 . If pedestrian  119  happens to see the truck  105  approaching, and the facility has provided safe zones such as safe zone  123 , then pedestrian  119  may be able to quickly move into the safe zone  123  along the path  124 . Safe zone  123  in this illustration has been produced by installation of physical barriers  121 , 122 . Fortunately, in this case, the fork truck  105  is shown to be equipped with a PDSC system  109  that will detect the personal alarm device (PAD)  125  being worn by pedestrian  119 . This detection will provide sufficient time to both the operator of the fork truck  105  and the pedestrian  119  being warned to allow the fork truck  105  to be slowed down and for the pedestrian  119  to move into the safe zone  123 . It should be noted that trucks may be in the adjacent portal areas, requiring the specific features disclosed here to avoid conflicts and confusion. Unfortunately, there can be significant complications and limitations present that will be described later and will be solved by the current disclosure. 
     Given that a docking portal has physical and operational characteristics that are different from most industrial arrangements, there are special functional features that are desirable in a proximity system, in addition to those that might typically exist for other materials handling operations. Therefore, it will be helpful to fully understand the desirable features of the combined PDSCs on the fork trucks, the PADs, and the DAC to work together. The following list highlights some key features of the collective system in a typical loading dock arrangement depicted in  FIGS.  1 ,  5 ,  6 ,  7 ,  9   . Subsequent paragraphs will then describe how PDSC, PAD, and DAC may function in order to provide these features. 
     1. Fork trucks on a roadway will detect pedestrians on or near the roadway, who are carrying PADs. The operator of the fork truck and the pedestrian will be given an alert when separation reduces to a range of from about 35 feet to about 40 feet, and a more significant alert when separation reduces to a range of from about 25 to about 30 feet. These alert ranges are adjustable and also are controllable by the PDSC. 
     2. Fork trucks that travel along roadways on a dock to deliver products to trailers being loaded and unloaded, if approaching another truck in the other lane, will provide brief alerts to the operators, by their PDSC systems. If one fork truck is trailing another, the PDSC will provide an alert to encourage the operators to adjust their speeds so that they are at least 30 feet apart. If a fork truck is parked at the side of a roadway, approximately perpendicular to the roadway, the fork truck in the roadway will be given an appropriate warning and the fork truck parked perpendicular to the roadway, or moving less than 2 feet per second, will be given a command by its PDSC to stop until the fork truck on the roadway is moving away or is out of range. However, if the PINGs indicate that the trucks are separating, there will be no warnings and no automatic action. 
     3. If a first fork truck has just exited from a portal area within the past five seconds, and it receives an ECHO that indicates a second fork truck is approaching, the PDSC on the first fork truck will determine from analysis of the magnetic field vectors or from compass readings if it is approximately perpendicular to the approaching fork truck. The first fork truck will stop or remain stopped until the second fork truck has begun moving away or is out of range. 
     4. Fork trucks that begin to turn off the roadway to enter a portal area will detect a DAC which will then change the mode of operation of the PDSC from a roadway mode or standard mode for operating in areas away from a portal area (standard mode) to a mode for operating in the portal area (portal modeportal mode). Upon activating the portal modeportal mode, the fork truck will slow to a lower speed, shrink its magnetic field, turn off the detection of the 3 millisecond magnetic pulses from other fork trucks, and reduce the duration of its PINGs and ECHOs so that they will not be detected by other fork trucks and to allow PADs to distinguish between trucks in the portal area from those in the roadway. All of the parameters can be adjusted to optimize for a specific facility. 
     5. Fork trucks in the portal mode will communicate with the DAC to acquire its identification (I.D.) and other information, which will be time stamped, and then be transmitted to the fork truck systems via RS-485 or CANbus. It will also be stored in a data module and then be automatically downloaded to a RELAY for transmittal to the Cloud, which will produce reports as requested. 
     6. The PDSC will analyze the ratio of the reference PINGs to the In/Out PINGs from a DAC, using DAC Electronics Module (DEM) to determine if the fork truck is entering into the trailer being serviced or is exiting out to the roadway. If the fork truck is determined to have exited from the portal area, portal modeportal mode will be terminated. 
     7. Design the Dock Area Controller to be quick and easy to install at a low cost. 
     8. The DAC will provide silent spots to generate silent spot fields, adjacent to the portal areas, within or generally coextensive with provided physical barrier safe zones, where the PADs will not respond to the pulsed low frequency magnetic fields from any trucks, whether in the roadway or in the portal area. 
     9. DACs will utilize concurrent transmission technology to ensure a very high reliability. 
     10. PADs carried by workers who are in the portal areas preferably respond to PDSCs on fork trucks in the portal areas but preferably do not respond to the PDSCs on fork trucks traveling on the roadway unless the workers get too close to the roadway. 
     SUMMARY 
     The present disclosure relates to a dock area control system including a vehicle having a vehicle proximity detection system (PDSC). The PDSC includes a vehicle low frequency magnetic field generator (MFG) that generates a vehicle pulsed magnetic field. The vehicle pulsed magnetic field defines a vehicle marker field, wherein the boundaries of the vehicle marker field are at an equal vehicle threshold strength of the vehicle magnetic field. The duration of the pulses of the vehicle pulsed magnetic field are selectable between a standard duration in a standard mode and a portal duration in a portal mode. The standard duration is different from the portal duration, the standard duration being about 3 milliseconds and the portal duration being about 2.3 milliseconds. A vehicle low frequency magnetic field detector is associated with the vehicle and detects pulsed magnetic marker fields and the duration of the pulses of pulsed magnetic marker fields. A vehicle radio frequency (RF) signal generator is associated with the vehicle and generates RF signals. A vehicle RF signal detector is also associated with the vehicle and detects RF signals. 
     The system also includes a dock area controller (DAC) having a dock electronic module (DEM), that generates a marking field. The DEM includes a microprocessor, a low frequency MFG that generates a pulsed magnetic field defining a DEM marker field. The boundaries of the DEM marker field are at an equal threshold strength of the magnetic field pulses. The low frequency MFG includes a reference component that generates a reference pulsed magnetic field oriented in a reference direction. An in/out MFG component generates an in/out pulsed magnetic field oriented in an in/out direction. The in/out direction is at a DEM MFG component angle to a horizontal reference direction. In certain embodiments, the MFG component angle is below a horizontal plane that includes the reference direction, wherein the MFG component angle is in a vertical plane that includes the reference direction. In certain embodiments the MFG component angle is preferably from about thirty (30) degrees to about sixty (60) degrees. The in/out MFG component is positioned a MFG component distance from the reference MFG component, wherein the MFG component distance is in the reference direction. In certain embodiments, the MFG component distance is preferably from about eight inches to about twelve inches. 
     The reference MFG component generates the reference pulsed magnetic field having a reference pulsed magnetic field duration, the reference pulsed magnetic field duration extending from a reference pulsed magnetic field start time to a reference pulsed magnetic field end time. The in/out MFG component generates the in/out pulsed magnetic field having an in/out pulsed magnetic field duration. The in/out pulsed magnetic field duration extends from an in/out pulsed magnetic field start time to an in/out pulsed magnetic field end time. In certain embodiments, the in/out pulsed magnetic field duration occurs after the reference pulsed magnetic field duration, wherein the in/out pulsed magnetic field start time occurs after the reference pulsed magnetic field end time. In certain embodiments, the in/out pulsed magnetic field start time occurs about the same time as the reference pulsed magnetic field end time. In certain embodiments, the reference pulsed magnetic field duration is preferably about one thousand (1000) microseconds. In certain embodiments, the in/out pulsed MFG duration is preferably about one thousand (1000) microseconds. 
     The DEM low frequency generator is electrically connected to the DEM processor and a tuned circuit that includes an inductor and a capacitor. A DEM magnetic field detector is associated with the DEM and detects magnetic marker fields, and detects the duration of the pulses of pulsed magnetic marker fields. A DEM RF signal transceiver including a DEM RF signal detector is associated with the DEM and detects RF signals. A DEM RF signal generator is associated with the vehicle and generates RF signals. 
     In certain embodiments, the system includes a safe spot low frequency MFG that generates a pulsed safe spot magnetic field defining a safe zone field, wherein the boundaries of the safe zone field are at an equal threshold strength of the safe spot magnetic field pulses. 
     In the standard mode, the PDSC generates a low frequency magnetic field standard PING for the standard duration, listens for a DEM ECHO for a DEM ECHO duration of approximately 1.25 milliseconds, listens for a PAD ECHO for a PAD ECHO duration of approximately 1.5 milliseconds, listens for a PDSC ECHO from other PDSCs for a PDSC ECHO duration of approximately 1.5 milliseconds, and switches to the portal mode upon receiving a DEM ECHO. 
     In the portal mode, the PDSC adapted listens for an RF signal, generates a low frequency magnetic field portal PING for the portal duration and concurrently generate a RF frequency data signal for the portal duration, listens for a DEM low frequency magnetic field PING for a DEM PING duration of 1.25 milliseconds, listens for a PAD ECHO for a PAD ECHO duration of approximately 1.5 milliseconds, determines the ratio of the field strength of the DEM PING during a reference half of the DEM PING duration divided by the field strength of the DEM PING during an in/out half of the DEM PING duration, determines based on the ratio the direction and/or speed of the vehicle, to generate an RF signal indicative of the direction and/or speed of the vehicle, and switches to the standard mode upon either no longer receiving a DEM ECHO or receiving instructions to switch by RF signal. 
     In the standard mode, the DEM listens for an RF signal, generates a low frequency magnetic field standard PING for the portal duration and concurrently generates an RF frequency data signal for the portal duration. 
     In the portal mode, the DEM listens for an RF signal, listens for a PDSC low frequency magnetic field PING ECHO for the portal duration, and generates an RF frequency data signal including instructions to the PDSC to switch to the standard mode. 
     Additional features, advantages, and embodiments of the disclosure may be set forth or apparent from consideration of the following attached detailed description and drawings. It should be understood that features of a single embodiment, or aspect, may be combined with features of another embodiment, or with other aspects. Moreover, it is to be understood that both the foregoing summary of the disclosure and the following attached detailed description are exemplary and intended to provide further explanation without limiting the scope of the disclosure as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic top view of one embodiment of a general layout of a loading dock, showing how fork trucks may maneuver; 
         FIG.  2    is a block diagram of one embodiment of a dock area controller electronics module (DEM) in accordance with the present disclosure; 
         FIG.  3    is a schematic view of one embodiment of a dock area controller (DAC) in accordance with the present disclosure; 
         FIG.  4    is a schematic view of one embodiment PDSC and PAD timing while exiting a roadway into a portal area; 
         FIG.  5    is a schematic top view of one embodiment of a layout of a loading dock, showing fork trucks exiting a roadway and entering a portal area; 
         FIG.  6    is a schematic top view of another embodiment of a layout of a loading dock showing DEM Fields and silent spots for trailer spacing of 12 feet; 
         FIG.  7    is a schematic top view of another embodiment of a layout of a loading dock showing DEM Fields and silent spots for trailer spacing of 15 feet; 
         FIG.  8    is a schematic view of one embodiment of DEM pulse timing and PDSC timing; 
         FIG.  9    is a graph showing ratios of the DEM magnetic fields; 
         FIG.  10    is a schematic view of a roadway showing a DEM adjacent to the roadway near a curve; 
         FIG.  11    is a detail schematic view of the DEM of  FIG.  10    taken generally along the line XI in  FIG.  10   , showing the arrangement of the ferrites that produce the DEM fields and detection points. 
         FIG.  11 A  is an end view of the DEM of  FIG.  11   ; and 
         FIG.  12    is a schematic view of one embodiment of a four way intersection having DEM/PDSC Control in accordance with the principles of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Three elements of the current disclosure are a PDSC integrated into a vehicle such as a fork truck, PADs which are worn by pedestrians and a DAC electronics module (DEM). The PDSC mainly provides the functions of a MFG/CAD which is discussed in detail in previous Frederick patents and space will not be used here to repeat that information. The DEM is a new device that alters how the PDSC and the PAD function and communicate, and cooperates with them to expand the overall system capability. In order to transmit data from the PDSC to the Cloud, a device, called a RELAY, is deployed that accepts data via Bluetooth and then transmits the data to the Cloud via a cell link. The result is a much smarter system for application to loading dock areas and to other areas in materials handling facilities. 
     The DEM disclosed here can communicate with PDSCs and PADs in both the low frequency magnetic field spectrum and the ultra-high frequency (UHF) radio frequency (RF) spectrum. Use of extremely high frequency (EHF) RF might also be possible without departing from the principles of this disclosure. This requires a way to generate and receive low frequency magnetic PINGs and ECHOs; and also transmit and receive higher frequency RF pulses.  FIG.  2    is a block diagram that depicts the electronic elements of one embodiment of a DEM  201  in accordance with the principles of this disclosure.  202 ,  208  produce PINGs and ECHOs of pulsed low frequency magnetic fields. Control of the generators  202 ,  208  is performed by a microcontroller  206 . As shown, three low-frequency inductor-capacitor (LC) circuits  203 ,  209 ,  213  each includes a wire-wound ferrite  204 ,  210 ,  214  and a capacitor  205 ,  211 ,  215 . Loops may be used in lieu of ferrites. One of these pulsed low frequency magnetic devices is a receiver  212 , which uses the LC circuit  213  to detect magnetic PINGs and ECHOs from other generators. The UHF transceiver  219  is connected to a UHF antenna  220 . Since the microcontroller  206  controls the functions of the generator  202 ,  208  and UHF RF transceiver circuitry  212  it has the capability of sending and receiving low frequency magnetic PINGs and ECHOs and RF emissions in many combinations as will be shown later. DEM  201  may further include at least one light emitting diode (LED)  218  that can be used to indicate operational state of the DEM or for any other suitable purpose. 
     In addition to marking locations, the DEM  201  also needs the capability to determine the direction of travel of vehicles within its range to transmit data related to the location that it is identifying and also acquire data related to vehicles and pedestrians within its range. The ferrite  204  is oriented parallel to the floor and is called the reference generator while ferrite  210  is oriented at approximately 45 degrees from the floor and is called the in/out generator  208 . Each generator  202 ,  208  produces a magnetic field pulse that is approximately 1000 micro-seconds long. The pulse length can be adjusted in combination with adjustments of other elements of the system. The PDSC on any fork truck passing under any DEM  201  measures the composite strength of each of these ferrites  204 ,  210  and calculates their ratio. The ferrites  204 ,  210  are also offset on the circuit board  221  in the longitudinal direction by approximately 8 inches to 12 inches. In the illustrated embodiment the circuit board  221  is planar and oriented in a vertical plane intersecting the trailer and the roadway  50 . The longitudinal direction is the direction towards the roadway  50  along the long axis of the reference ferrite  204 , and may be referred to as the reference direction. The reference ferrite  204  is positioned closer to the roadway than the in/out ferrite  210 , in the longitudinal direction. The reference ferrite  204  may be positioned lower than the in/out ferrite  210  on the circuit board  221  to increase the separation of their respective magnetic fields as sensed by the PDSC on the fork truck. For example, the reference ferrite  204  (oriented about horizontally) may be placed at the front bottom of the circuit board  221 , and the in/out ferrite  210  (oriented down at about 45 degrees) may be placed at the rear top of the circuit board. The offset accentuates the comparative readings because the field strength decreases at a rate proportional to the cube of the distance. PINGs are sent from the two ferrites  204 ,  210  at a statistically produced rate having an average spacing of approximately 200 milliseconds. By operating the two generators  202 ,  208 , with generator  208  following immediately after generator  202 , it is possible to compare the ratio of the signal strengths in a short period of time, namely within the aggregate length of time of the two PINGS which is 2 milliseconds. As a fork truck passes under the DEM  201 , the ratio of each pair of readings can be compared. If the truck is moving one direction relative to the DEM  201 , the ratios calculated in the PDSC on a fork truck will be markedly different than if the truck is moving in the opposite direction. Thus, the DEM  201  allows the PDSC on the truck to determine with certainty which direction it is moving. 
       FIG.  9    depicts an example of the ratios that may be produced by an embodiment of this process. Referencing  FIGS.  2 ,  5  and  9   , an example setting of parameters may be as follows for a DAC system  500  for an exemplary trailer portal facility as described herein. Other settings might be chosen for a similarly or differently configured facility. The software in the PDSC  505  of the fork truck  501  will recognize magnetic fields  513  from the DAC  529  and DEM  201201  at approximately 10 to 12 feet when the strengths of the two fields, produced by the two ferrites  204 ,  210 , exceed a voltage threshold in the PDSC  505  that has been selected at the factory or as adjusted with the UHF wireless configuration tool  224 . The PDSC  505  will also produce a ratio value indicative of the PDSC-sensed reference field strength divided by the PDSC-sensed in/out field strength (R/IO Ratio). Alternatively, in other embodiments, the PDSC  505  may produce an inverse ratio value indicative of the sensed in/out field strength divided by the sensed reference field strength. In the illustrated embodiment, the R/IO Ratio is determined by the software in the microprocessor  206  of the PDSC  505 , however in other embodiments, hardware electrical components may be used, particularly in non-variable environments where adjustment of set-points is less desirable. In the illustrated embodiment, the R/IO Ratio between the strengths of the two fields produced by the two ferrites  204 ,  210  in the DAC  529  DEM  512 , is greater than 1.1 when the PDSC  505  is positioned between the DEM  512  and the roadway  524 . DEM  512  is constructed in the same way as DEM  201  described above. And the R/IO Ratio is less than 1.1 when the PDSC  505  is positioned between the DEM  512  and the trailer  527 . When the PDSC  505  is approaching the DEM  512  from the direction of the roadway  524 , the R/IO Ratio will increase rapidly as the PDSC  505  passes under the DEM  512 . The R/IO Ratio will be less than 1.1 when approached the DEM  512  from the direction of the trailer  527  and will reduce to a smaller ratio before beginning to rise as the PDSC  505  passes under the DEM  512 . When moving from under the DEM  512  to away from the DEM  512 , going toward the roadway  524 , the R/IO Ratio will initially be high and will reduce toward a value slightly above 1.1. If leaving the DEM field  513  while going into the trailer  527 , the R/IO Ratio will rapidly reduce to a minimum value and then rise toward a value slightly under 1.1. A reliable logic that provides a margin for error is: A change in the R/IO Ratio from a value above 1.25 to the value of 1.25 will result in the state “exiting to roadway.” A reduction from a value below 1.25 down to a value of 0.85 or less will establish the state “entering a trailer.” Once a state has been established, it will be retained until the DEM field  513  strength at the PDSC  505  drops below the discriminator setting or the R/IO Ratio exceeds 1.6. 
     Adjustments to the parameters in DEM  201  can be made with the UHF wireless configuration tool  224  and small adjustments can be made with a magnetic switch  216 . All the DEM  201  functional elements are placed on a Printed Circuit Board Assembly  221 . The Printed Circuit Board Assembly may be placed in any suitably sized non-metallic enclosure  223 . 
     In order to reduce hardware cost and installation cost, a novel and simple mechanical configuration of the DAC assembly is depicted in  FIG.  3   . Shown is a segment of a DAC system suited for docking ports. Polyvinylchloride (PVC) electrical junction boxes  303 ,  305  are connected by PVC electrical conduit  306 ,  307 ,  308 ,  310  to correspond to the spacing of the trailer portals with junction boxes assigned to individual portals.  FIG.  6    shows the spacing between the junction boxes for the DEMs  604 , 606 , 608  and the silent spot fields  612 ,  613  for a facility that is configured for the trailers in portals adjacent to one another to be spaced each 12 feet, the minimum spacing allowed. Each DEM in the DAC is enclosed in a non-metallic housing that is attached to the junction boxes.  FIG.  7    gives the dimensions for a facility that positions the adjacent portals every 15 feet along the dock indicating the location of the junction boxes and associated DEMs  704 , 706 , 708 . DEMs  704 ,  706 ,  708  are constructed in the same way as DEM  201  described above. Note that in  FIG.  6   , that when the truck  602  is on the left side the nearest PDSC  610  passes to the field from DEM  608  is 26.3 inches. If the truck is on the right side, the nearest it passes to the field from DEM  606  is 27.7 inches. DEMs  606 ,  608  are constructed in the same way as DEM  201  described above. This should be adequate margin to allow for slight errors that might be made in the positioning of the DEMs in the DAC. By reducing the size of the fields of the DEMs, the margins can be increased. Referring to  FIG.  7   , where the trailers are all spaced 15 feet apart, the margins are much greater. When truck  702  is in the left position, there is 62.3 inches margin between the field  709  of DEM  708  and the PDSC  710 . When truck  702  is on the right side, the margin between the field  707  of DEM  706  is 63.7 inches. 
     It is preferable for safe zones to be provided at the edge of the portal areas. For example, safe zones are depicted in  FIG.  5   . Silent spot field  523  is produced by a silent spot  522  that is positioned midway between safe zone barriers  520 ,  521 . The positioning of the junction boxes  303 ,  305  is established by the length of conduit  306 , 307 , 308  and all similar segments of conduit along the length of the DAC system  500 . Most facilities place all the portals with a fixed spacing so that the conduit segments would be the same length. However, if there are variations in the portal spacing, this is easily compensated for by adjusting the lengths to place the junction boxes in the optimum location. If the portal spacing is wider, the positioning is less critical as explained in the above paragraph. A simple chart can be made to show the needed distance from one side of the portal area. 
     Since all the elements of the necessary to install a DAC system would typically be standard electrical components typically used by most any electrical contractor, assembly should be quick and not require any special documentation other than the distance from one side of the area and a height for the DAC system to be suspended above the portal area. The conduit will only contain two wires to carry a small amount of electrical power for powering all DEMs and silent spot circuits. Power will be low voltage, such as 12 volts direct current (VDC) by a commercially available power supply. A single supply may provide power for up to 50 portals. Fork trucks that are suitable for loading trailers preferably have short masts so that height of the DEM can also be low, only providing for an appropriate amount of clearance. As shown in the  FIG.  3   , a typical height for the silent spot would be about 7.0 feet, slightly taller than any pedestrians. However, this is not critical and can be changed by adjusting the size of the silent spot field from the silent spot. Similarly, the DEMs should be approximately two feet above the PDSCs on the fork trucks and this can be adjusted as well. Most of these considerations are intuitive and easily determined when the facility is surveyed by an engineer or trained technician. Silent zones and silent spots are described in previous Frederick patents. 
     The following paragraphs describe how the PDSC, PAD, and DAC operate in a cooperative and sequential manner to accomplish the functions of the element configurations summarized above. Other, detailed performance features that make the PDSC and PAD systems more reliable, more accurate, and user friendly are described in earlier Frederick patents. Integrated functionality accomplished through synchronized communications between elements, combined with utilization of two widely separated spectrums create a novel composite system that accomplishes safety enhancements and acquires highly reliable data. 
     One way to visualize how this system functions is to begin by discussing fork trucks equipped with PDSCs that are traveling along a roadway, then describe the actions and responses at the time that the truck turns into a portal area, then describe how the system elements cooperate while the PDSC is in the portal area, and, finally, describe how the system elements interact and cooperate as the truck with its PDSC exits from the portal area into the roadway. 
     Turning now to  FIG.  5   , while fork trucks are traveling on a roadway  524 , it is imperative that the PDSCs  505 ,  506 ,  507 ,  508  on the fork trucks  501 ,  502 ,  503 ,  504  provide for pedestrian proximity detection and collision avoidance capabilities. For example, if pedestrian  519  strays onto or crosses the roadway  524 , vehicles on the roadway  524  such as the fork truck  504  should detect the PAD  125  carried by the pedestrian  519  and then take actions. The actions may be for the PDSC  508  to give an alarm to the operator of the fork truck  504  and the PAD  125  to give a warning to the pedestrian  519 . The actions may also include automatically slowing or stopping the truck  504 , depending upon the details about the facility operation. Also, fork trucks following too closely together as indicated by fork trucks  502  and  503 , the operators should be given a special warning so that they will adjust their speeds to provide more separation. Operators should also be given some kind of non-offensive alert, possibly a couple of short, soft beeps, when they are approaching another fork truck head-on such shown by fork truck  504  approaching fork trucks  501 , 502 , 503 . These steps can be taken because repetitive readings of the ECHOs can be used to determine the rate of approach or separation. 
     An important characteristic of using low frequency magnetic fields is that they provide proximity detection for all 360 degrees around a vehicle. This is important because there are many types of accidents other than a pedestrian or truck being directly in the path of travel of a second truck. Fork trucks sometimes push objects against pedestrians, pinching or crushing them. Payloads sometimes fall from truck forks and strike pedestrians. Feet are crushed after a pedestrian has been standing at the side of a stopped truck. It is also important that the range of the low frequency magnetic fields be sufficient for the speed of the vehicles and for the arrangement of the facility. In situations as depicted in  FIG.  5   , where trucks may be traveling at maximum speed allowed by company policy, the range of the magnetic fields need to be large to give time to respond to a detected danger. In this situation, the sides of the magnetic fields extend from the roadway  524  into the portal areas  525 , 526  and possibly even into the back of the trailers  527 , 528  and others. Persons working at the back of the trailers  527 , 528  such as pedestrian  518  will be inside the magnetic fields  509 , 510 . They will be alarmed, if not inhibited, and so will the operators of passing fork trucks  501 , 502 , 503 , 504 . They should not be alarmed because they are safe when near the trailers. If they move toward the roadway  524 , at some point, they should be alarmed because they can be in danger. So, the challenge is to provide detections, alarms, and actions when they are needed but only when needed. Essentially, what is needed is for the PADs  125  carried by pedestrians working near the trailers to respond to trucks arriving at the portal where they are working but not to respond to trucks traveling along the roadway. This requires a more complex, smarter system than previously available. 
     The DAC  529  includes DEMs  512 , 514 , and others along the dock. These DEMs  512 , 514  are constructed in the same way as DEM  201  described above and will modify the way that the PDSCs on the fork trucks function and also change the way that any PADs  125  in their range function. This will be explained in the next section. 
     DEMs in the DAC preferably do not respond to trucks that are traveling along the roadway  524 . This is made possible by reducing their sensitivity to not detect the PINGs from any trucks on the roadway. One aspect of the DEM design is that the ferrite  214  is oriented perpendicular to the roadway and the magnetic fields at the trailers from PINGs produced by PDSCs in the roadway are parallel to the roadway in the area behind the trailers. This perpendicular orientation, minimizes magnetic coupling to the PINGs. As a truck begins to turn into a portal area, its PDSC begins to get closer to the DAC and the orientation of the PING field begins to no longer be perpendicular. This change in orientation quickly boosts the magnetic coupling so that the DEMs in the DAC begin to detect the PINGs from the PDSC  505  on a truck  501 . 
     It should be noted that during all phases of operation, PADs  125  outside the portal areas respond to trucks and PADs in the portal areas respond to trucks in the portal areas and send data packs that report proximity events for that PAD. PDSCs also report events. This information is immediately transmitted to the truck data system via RS-485 or CANbus standards for reporting along with other truck information. It is also sent to a data module which stores the data until the truck is within the range of a RELAY  217  (see  FIG.  2   ) which will acquire the data via Bluetooth and then automatically transmit the data to the Cloud for reporting. Proximity events related to trucks in close proximity with each other are handled in a similar manner. 
     If a fork truck  501  begins to turn off the roadway and into a portal as shown in  FIG.  5   , the magnetic field  511 ,  513  from its PDSC  505  will begin to reach the DEMs  512 ,  514  in the DAC  529  with enough strength so that the DEMs will begin to respond by sending ECHOs that are received by the PDSC  505 . These ECHOs will have timing parameters different from standard ECHOs so that the PDSC  505  will recognize that they are from a DEM, rather than from a PAD or CAM. After multiple ECHOs are received, such as for example a total of three, the PDSC  505  will determine that it is entering the portal area and switch to the portal mode. 
     Timing parameters for the PDSCs, PADs, and DEMs are depicted in  FIG.  4    and  FIG.  8   .  FIG.  4    shows how the parameters change as a fork truck turns off a roadway into a portal area.  FIG.  8    gives more detail on timing parameters between the elements once a fork truck has entered into the portal area. 
     In order to understand the operation of the system, it is necessary to understand that the basic principle that the system elements each operate asynchronously; yet, are designed to minimize conflicts by use of fixed timing sets and concurrent transmissions. One advantage is that this approach allows each fork truck and each person wearing a PAD to be more independent, giving each person and each operator the confidence that they are in control of their own safety without dependence upon a centralized system that may fail to recognize or respond to the unique circumstances encountered. Importantly, if there is a problem with a PDSC, the fork truck can be sidelined while being repaired without disrupting other elements in the facility and without requiring the vigilance of special operators for a centralized system. 
       FIG.  4    shows that a PDSC  505  on a fork truck in the facility will be generating magnetic fields in a repetitive semi-random manner. It then has timing windows in which it expects to receive responses, called ECHOS, from PADs, or from other fork trucks. When in a portal area, it also has a window in which it expects that it may receive ECHOs from DACs. The left portion  401  of the  FIG.  4    shows the key points in time for a fork truck that is on a roadway or other part of the facility, other than in a portal area. The right portion shows the modified timing after entering a portal area, the point of switch being indicated by  405 . 
     Key timed actions by the PDSC  505  on a fork truck are shown in the upper portions  401 , 402  and the timed actions by the DEM  201  are shown in the lower portions  403 , 404 . 
     Beginning with the upper left section of the  FIG.  4   , a PDSC  505  on fork truck  501  generates a 3 millisecond low frequency magnetic field  406 . Afterwards, it has timed windows, created in the PDSC  505 . One window  407  is designated for any ECHOs from a DEM, one window  409  for any ECHOs from PDSCs of other trucks, and one window  408  for ECHOs from any PADs. Each element is programmed to produce ECHOs that correspond in time to match the windows. In this portion  401  of  FIG.  4   , it is assumed that the fork truck of interest is not within the portal area but as the fork truck begins to turn into a portal area, one or more of the DEMs  201  on the DAC will begin to echo back to the PDSC  505  on the fork truck. If a sufficient number of ECHOs are received, the PDSC  505  on the fork truck will switch at time  405  to the portal mode, the timing being shown in  402 . 
     Prior to changing to the portal mode, any ECHOs from a PAD or other PDSC on another fork truck will be responded to and the appropriate safety action will be taken and that proximity event will be recorded in the data. 
     Once a sufficient number (for example for some systems two or three may be sufficient) of DAC ECHOs are received by the PDSC  505 , it will switch from the standard mode  401  to the portal mode  402  and the timing system will switch to the timed events shown on the right portion  402 . In the portal mode, the PDSC  505  will listen for approximately 500 micro-seconds, shown as time  410 , for any UHF signals that are above the set threshold. If none are detected, it will begin transmitting a UHF signal  411  to block other PDSCs in nearby portal areas from generating PINGs, and will begin to generate a PING  412  with a duration less than that for systems outside the portal area, typically 2.3 milliseconds. If a UHF signal is detected, it will delay its action for a few milliseconds, determined by a statistically controlled timer in the PDSC  505 . PINGs generated by PDSCs outside the portal area, being 3 milliseconds in duration, will be ignored by PDSC  505  in the portal area. Likewise, any PINGs generated by PDSCs inside the portal area, being approximately 2.3 milliseconds in duration will be ignored by PDSCs and PADs outside the portal area. Timed windows are provided for PAD ECHOs and DAC ECHOs. 
     The lower left portion  403  of  FIG.  4    shows how the DEM is timed when it is not receiving any 2.3 millisecond PINGs from a fork truck in its range and the lower right portion shows how the DAC  512  responds if a 2.3 millisecond PING is received. 
     Some of the most pertinent information regarding this disclosure is the communications that occur once a DEM responds to the PINGs which causes a PDSC to switch to the portal mode, at time  405 . Exchanges of PINGs and ECHOs between the elements involved are then accomplished to a different timing protocol as indicated in the time frame  402  in  FIG.  4   . Once in the portal mode, the DEM issues two millisecond PINGs, divided into two parts, one part being issued from the ferrite that is parallel to the floor and the other ferrite being at approximately 45 degrees relative to the floor. Other PDSCs on other fork trucks, and PADs outside the field of a DEM, will not respond to this pair of PINGs. But, PADs  125  inside the field of a DEM will respond unless they are positioned within a safe zone that is equipped with a silent spot. 
     Once the PDSC  505  has switched to the portal mode, it will take five actions: (1) it will give a command to the fork truck  501  to reduce its speed to a specified maximum speed, (2) the power to the low frequency generator  202  will be reduced in order to reduce the range of the PDSC, (3) PINGs will be changed to only be 2.3 millisecond duration so that fork trucks in close proximity will ignore the PINGs, (4) it will stop detection of 3 millisecond PINGs from other fork trucks, and (5) it will begin listening for UHF RF pulses and associated low frequency PINGs that are produced by the DEMs. Use of the UHF pulses allows a more precise timing arrangement so that the multiple exchanges of signals can be accurately coordinated. Also, the data transfer can be accomplished within the available time. Higher RF frequencies provide even greater precision and allow more data to be output. 
     Reduction of the speed of the fork truck  501  gives the pedestrian  518  more time to move out of the path of the truck. It is normally good practice to move more slowly as the trailer is approached. Reduction of the power in the PINGs reduces the chances of the PDSC  505  alarming a PAD carried by a pedestrian in an adjacent portal area. Changing the duration of the PINGs prevent any trucks on the roadway from being affected by the truck  501  which is safely in the portal area. Once in the portal area, the remaining tasks are related to communicating with the DAC and any pedestrian in the area. 
     It is desirable that special safe zones be provided in locations that are adjacent to the portal area so that a pedestrian can quickly move into the area but also remain close by. Junction boxes  303  are spaced along the DAC  301  so that they will be positioned at the interface of portal areas where it is practical to provide barriers to produce safe areas. The silent spot  322  is attached to the junction box  303  and will mute the PADs  125  carried by any pedestrian at that location so that no warnings will be given to the pedestrian or the operator of the truck. 
     Design of the DAC system and the sizes of the fields are chosen to be compatible with the arrangement of a facility. Usually, there is a high degree of consistency between portal areas so that once a system configuration is selected, it will be repeated at each portal. If a distribution center has 200 portals and they are all identical, then once the parameters and dimensions are set for one portal, all others can be replicated. However, adjustments can be made on site to accommodate variations. 
     As shown in  FIG.  6   , a fork truck  602  may enter the portal area  601  on the right side or on the left side of the portal area, or anywhere in between. The fork trucks in this disclosure are assumed to be small, stand-up types but could be any type truck that is low enough to enter into the trailers. Correct positioning of the DEM is preferably somewhat more precise for narrower trucks since there is a wider range of possible PDSC locations and the separations between the adjacent portal areas are smaller. For best operation on a loading dock, the PDSC units should be located on the same side of the fork truck, preferably near the top of the canopy, and as near the longitudinal center of the truck as practical. DEMs would be positioned approximately midway between the most extreme left/right positions of the PDSC within the portal area in which the truck is located.  FIG.  6    shows proper positioning for the minimum trailer spacing of 12 feet and  FIG.  7    shows the larger margins for trailer spacing of 15 feet. 
     Magnetic pings with concurrent UHF pulses will be produced by DEMs  604 ,  606 ,  608 ,  704 ,  706 ,  708  at least two times per second but not more than about six times per second. As in the other embodiments described above, DEMs  604 ,  606 ,  608 ,  704 ,  706 ,  708  are constructed in the same way as DEM  201 . These magnetic pings and UHF pulses will determine when the PDSCs  610 ,  710  on the fork trucks are within the precisely defined range of the DEMs  604 ,  606 ,  608 ,  704 ,  706 ,  708  but will also alter how the PADs  125  within the DEM range respond to PINGs. Once communications have been established by at least two link-up cycles, data can be sent to the PDSC  610 ,  710  from the DEM with very high reliability. Once the PDSC  610 ,  710  is positively confirmed to be within the DEM  604  range, the DEM will begin sending UHF pulses concurrent with its PINGs, which are produced in two segments. This will be explained better later and is illustrated in  FIG.  8   . Once a PAD  125  is within the range of a DEM  604 , it will recognize the 2.3 millisecond PINGs and the concurrent UHF pulses and switch to the portal mode. While in this mode, it will not respond to the 3 millisecond pings from trucks in the roadway unless near the roadway, because the detection levels will be increased. When in the portal mode, they will respond to 2.3 millisecond PINGs and concurrent RF pulses from trucks that have entered the portal mode. 
     Fundamental to the cooperative functions between PDSCs, DEMs, and PADs is the timing of the elements. In order for pedestrians to be protected from incoming fork trucks while not disrupting normal travel on the dock roadway, for fork trucks in the portal areas to not affect or be affected by fork trucks on the roadway, for DEMs to not be confused by PINGs and RF transmissions from PDSCs in adjacent portal areas, and to acquire data with precision, an organized means of communication is necessary. At the same time, low power from all elements is desirable to minimize the ambient RF and magnetic noise in the facility. 
     Concurrent PINGs and RF transmissions from the DEMs such as DEMs  512 ,  514  are typically produced semi randomly with a minimum rate of about 2 per second and a maximum of approximately 6 per second. 
     Once the PDSC  505  has switched to portal mode, it begins to operate as required for that mode, rather than the standard mode required for being on the roadway  524 . Once a PAD  125  is carried into the range of a DEM  512 ,  514 , the PAD will respond to PINGs that are either 2.3 milliseconds long or 3 milliseconds. However, they will only respond to the danger level voltage (range) for 3 millisecond PINGs. Also, when 2.3 millisecond PINGs are received from a fork truck in the portal area, it will respond to the PING voltage level (range) that has been chosen for the configuration of the loading dock. If a pedestrian  518 ,  519  wanders out toward the roadway  524 , they will begin to be warned by fork trucks on the roadway before reaching the roadway and but they will also continue to respond to trucks that enter the portal area. Note that the reduced PING duration of 2.3 milliseconds can be a different duration by altering the PING rejection criteria and making other adjustments. 
     In order to ensure high reliability, concurrent transmissions will be utilized. Precise RF transmissions will establish a timing reference that cannot be obtained from low frequency PINGs. For example, it is important to know with confidence whether a truck is traveling toward the trailer or traveling toward the roadway. It is also important to know with certainty that data being acquired is from the portal area in which a truck is located and not from an adjacent portal area. The timing chart in  FIG.  8    explains how this is accomplished with reference to the DAC system configuration shown in  FIG.  5    and indicates the precision preferred. 
     As shown, DEM  512  will have had its LF pulsed magnetic field  513  set by use of the adjustment tool  224  so that the range will fall short of reaching the PDSCs  505  in adjacent aisles. All DEMs  512 ,  514 ,  516  in the DAC will be elevated above the floor to allow low-profile fork trucks  501 ,  502 ,  503 ,  504  to pass under on the way to and from the trailers. For example, for a typical height of the canopy of about 7.5 feet, the DEM  512 ,  514 ,  516  height may be about 10.5 feet. 
     DEM  512  and PDSC  505  timing parameters are depicted in  FIG.  8   , but can be adjusted in multiple ways in order to be optimized for the specific hardware elements being used. In order to have maximum confidence in the connection between the DEMs  512 ,  514 ,  516 , PADs  125  and PDSCs  505 , a burst sequence can also be incorporated as described in earlier Frederick patents. 
     Numerous, precisely timed RF Pulses and magnetic PINGs cooperate together so that the DEM and the PDSC will establish with high reliability that a specific pair of fork trucks and DEMs are communicating only with each other. Precise timing also allows data sets to be sent from the DEM  512  to the PDSC  505  meshed in with the PINGs and RF pulses. 
     The embodiment of the timing profile shown in  FIG.  8    begins with the DEM  512  listening for 500 micro-seconds, terminating at the point  802 , to verify that there are no other nearby DEM or PDSC  505  systems in operation. If another system is in operation, the DEM  512  will delay a statistically determined amount of time before attempting to transmit. Without this statistical factor, there could be a pileup immediately following the completion of a cycle. The cycle would be initiated at time  803  by the transceiver in the DEM  512  beginning to emit 916 million cycles per second (MHz) for a total of 750 micro-seconds to a time  804 . If there was no on-going PDSC activity prior to start of the current sequence, the PDSC  505  on truck  501  would be listening as was the DEM  512 . The PDSC  505 , will detect the DEM  512  signal and continue to listen for the signal to terminate, which is time  804 . The PDSC  505  will recognize that the 73 thousand cycles per second (kHz) PING began at 250 micro-seconds after start of the 916 carrier and interpret these signals as originating from a DEM and will begin recording the magnetic PING at time  809 , which corresponds to time  805 . Since the magnetic fields have been separated, there will not be a conflict with other DEM magnetic fields. The actual I.D. of the DEM  512  will be transmitted to the PSDC  505  later in the sequence. 
     After the DEM  512  has completed its 916 MHz at time  804 , and has initiated the 73 kHz at the expected time for a DEM, the PDSC  505  will initiate a 916 MHz ECHO that starts immediately following the termination of the time  804 . Meanwhile, the DEM  512  will have been expecting an ECHO to arrive at its RF transceiver at time  816  and terminating at time  817 . Having completed these steps, both the PDSC  505  and the DEM  512  will have confirmed that the two units are linked and can continue into Phase III. 
     Two main objectives are to be satisfied by Phase III. A time slot is established during which the DEM can transmit its I.D. and a small amount of other data. If other PADs  125  are in the range of the DEM  512 , their I.D.s will also be sent in a second 7 millisecond data pack. And, time has been provided for the second period of low frequency (73 kHz) generation. The reason for the two separate PINGs, time  805  to  806  and time  814  to  815 , is to allow determination as to whether a fork truck is entering the DEM  512  field to service a trailer or if the fork truck is leaving the portal area after servicing the trailer and is moving toward the roadway  524 . This is preferable for two reasons. First, if the fork truck is headed toward the roadway, its mode of operation should be changed quickly in order to provide the most useful signals to the operators of other fork trucks in the roadway and also so that the driver of fork truck  501  will be alerted in the most effective way. This situation will be discussed further in later paragraphs. The second reason is to be sure that the data being acquired is accurate. After a fork truck begins to enter deep into a long trailer, the PDSC will exit the DEM range and the data system will report that the fork truck has left the area after servicing the trailer. Then, when the fork truck backs out of the trailer and re-enters the DEM range, it will report a second visit to the portal area. To solve this problem, the DEM has two separate low frequency magnetic field generators that cooperate to make it possible to distinguish which direction a fork truck is exiting the DEM field. Once it is determined that the fork truck  501  has exited the portal area, the PDSC  505  will emit an ECHO at time  819 , which the DEM  512  will be awaiting to receive. Once complete, both the PDSC  505  and the DAC DEM  512  know that the fork truck  501  has left and they re-set for the next cycle. 
     It should be noted that the data acquired from servicing a trailer is first stored in the PDSC  505 , then automatically transmitted to the fork truck  501  via RS485, and then sent via a RF RELAY to the Cloud. 
     In order to know whether the PDSC on fork truck has left the field of the DEM because it is entering the trailer or because the truck is returning to the roadway, the DEM has two ferrites  204 ,  210  for generating magnetic pings. Ferrite  204  is oriented parallel to the floor. A second ferrite  210  is tilted at 45 degrees relative to the floor. As shown in  FIG.  8   , each ferrite  204 ,  210  is commanded in sequence. Since the DEM  512  is positioned above the PDSC  505 , the strength of the tilted ferrite will vary in strength relative to the level ferrite, indicating which direction that the PDSC is moving. Having this information allows making a quick decision upon leaving the field headed toward the roadway to exit the portal mode and return the PDSC  505  to the standard operating mode before entering the roadway. Also, if the PDSC  505  exits the DEM  512  field due to the truck driving into the trailer, the data can be tagged so that it will correctly report that the truck only entered the portal area one time. It would be possible to report both events if desired. 
     Power levels from the RF transceiver  215  in DEM  201  should be only as high as needed for reliable communication within the portal zone, as good design practice. RF radiation reduces according to the square of the distance and it will reflect off of metallic surfaces. The result of the characteristics of RF is that in order to achieve a highly reliable transmission, the RF power level must be high enough to reach from the source to the receiver, with a substantial margin. In comparison, low frequency magnetic fields can be controlled with considerable precision due to the rapid rate at which the field strength reduces (according to the cube of the distance) and since the magnetic field will not be reflected from metallic objects or surfaces. 
     After servicing a trailer, a fork truck will back out of the portal area, motor first, with forks trailing. The PDSC should be located near the canopy of the fork truck and as near the center of the fork truck as practical. All fork trucks in the facility need to have their PDSCs to be mounted on the same side of the fork truck, as explained earlier. As a fork truck backs out of a portal area into a roadway, there is a potential for a collision with fork trucks already traveling on the roadway. In  FIG.  1   , fork truck  112  depicts a fork truck that could either be entering or exiting the roadway  50 . If exiting, fork truck  111  needs to be warned. However, a PDSC on truck  112  would not know if truck  112  was parked at the entrance of the portal area  104 , preparing to enter portal  104  to service trailer  108  or was making ready to exit onto the roadway  50 . 
     When fork truck  112  is inside the edge of the portal area, it will generally be oriented perpendicular to the roadway  50 . If it is not moving or is moving very slowly so that its direction of travel is not certain, the operators of both fork trucks  111 , 112  should be given a special warning about this uncertain situation. Most roadways at large loading docks will be oriented in one general direction and that knowledge can be programmed into the PDSC  120 . The compass inside the PDSC  120  can determine if the fork truck  112  is generally perpendicular to the roadway so that the driver of that fork truck can be given a special warning that there is another fork truck nearby on the roadway, assuming they are moving toward each other. The PINGs from the PDSC  120  can determine if the two fork trucks  111 , 112  are moving toward or away from each other by the changes in the strength of the PINGs. If they are moving apart, no warning is needed. Techniques, using the existing capabilities of the PDSCs on the two fork trucks can be used for alerting the fork truck  111  on the roadway, assuming an alert is needed. 
       FIG.  6    shows a fork truck  602  that has entered portal area  614  and has almost reached the magnetic field  615  that is produced by DEM  604 . As the truck  602  continues into the DEM  604  magnetic field, the communications between the DEM  604  and PDSC  610  will proceed as described in the timing chart,  FIG.  8   . Once the PDSC  610  has confirmed that the start and stop times for the RF pulses and the low frequency PINGs are at the correct times, it sends a 916 MHz ECHO. When the DEM  604  receives the ECHO  810 ,  811  into its receiving window  816 ,  817 , it confirms that the link up is complete and valid. Knowing that the timing is valid, data transmission from DEM  604  to PDSC  610  begins at time  812  and ends at time  813 . There are options on how to establish the duration of this data transmission. For the configuration and timing contemplated for the arrangement disclosed in this current disclosure, the duration would typically be about 7 milliseconds to allow transmission of the I.D of the responding device and the I.D. of the PDSC, and the time stamp for the time of this proximity event. However, if there are PADs  125  within the range, transmitting their IDs will require additional time so that a 14 millisecond transmission would be used for that specific transmission. The PDSC  610  will send an ECHO that confirms receipt of the transmission. PDSC  610  immediately sends the data to the fork truck  602  via RS485 or CANbus. Once within range of a RELAY  217 , the PDSC  610  will send the data to the Cloud via the RELAY. A crucial piece of data to be sent is the I.D. of the DEM  604  and the time that the linkup was made. 
     Pulsed low frequency magnetic fields produced by the DEM in the DAC assembly define a precise field that can be used to report to the cloud the specific fork truck I.D. If management agrees to allow the name of personnel to be correlated to the PDSC that they are operating or the PAD they are carrying, this information can be included in reports produced in the Cloud. Additions of precisely coordinated UHF communications can not only transmit this information, and possibly other information such as information about the trailer being serviced, but when used in precisely time cooperation with the low frequency pulses, can provide an extremely high reliability data system. Visible and/or audible warnings can be given if the fork truck is not intended to enter a trailer because, for example, its mast might be too tall. Such warnings may require a modification to the DEM for that purpose, but the functional capability exists within the DAC architecture. 
     In various embodiments, the DAC system  500  may be used to measure the speed of a vehicle, and if it is moving too rapidly, to give an alarm and/or give instructions to the vehicle to reduce speed. For example, the DEM microprocessor  206  may generate successive PINGs from the generators  202  and  208 . If a vehicle is close enough to be in range of the PINGs, its PDSC will respond with ECHOs. The microprocessor  206  may initiate an exchange of two more PING/ECHO sequences to confirm that the signals are valid. Once that has been confirmed, the microprocessor  206  may send a data set through the UHF transceiver  219  to notify the PDSC that its speed is to be measured. The PDSC will begin to sense the pulses and measure their strength. The period of time between pulses can be pre-set or it can be transmitted to the PDSC via the data set. For purposes of this illustration, assume that a total of five pulses are sent, spaced 50 milliseconds apart. The amplitude of the oscillating magnetic field being sensed by the PDSC will increase inversely proportional to cube of the distance. The distance at which the PDSC will sense the magnetic field is pre-programmed and known (such as the distance for a warning zone, or a danger zone), the distance is known at which the speed calculations will begin. The microprocessor will then calculate the speed at which the vehicle is moving between each pulse. The readings will be averaged and compared to the value set into the DEM for this location. A suitable speed limit might be five (5) feet per second. Assuming that the magnetic field is adjusted to produce a magnetic that is approximately twenty (20) feet in diameter for the predetermined distance, then during the 200 milliseconds from the first pulse to the fifth pulse, the truck would move one foot. During that time the strength of the magnetic field would increase approximately by the cube of ten divided by nine (10/9), or thirty seven percent (37%). This should allow a sufficiently accurate speed measurement for most situations. If more accuracy is desired, the measurements can be fitted to a curve, more pulses can be sent, and/or the size of the magnetic field can be increased. The PDSC would be programmed to recognize if the speed exceeds five (5) feet per second. If so, it would flash the PDSC warning lights on the vehicle to alert the operator that the vehicle is moving too fast for this location, or automatically reduce the vehicle speed. Other embodiments may measure speed in locations other than the portal, such as in the roadway. 
     Again, the added function features described above take advantage of the elements and system capabilities of a typical pulsed low frequency magnetic field proximity detection system. For example, a DEM at emergency doors can record and transmit information about pedestrians that have passed through those doors, including direction of travel. Similarly, movements of pedestrians and fork trucks through doors or passage ways to areas that are restricted in some way can be tracked or can be inhibited by alarms or gates. DEMs located at the start of a sharp curve in a roadway can force a fork truck to a slower speed. Fork truck types that are too tall for a passageway can be stopped before collision. DEMs located at major pick up points and major dump points can be used to measure and report minimum, maximum, or average travel time for one or all vehicles. Objects near roadways can be tagged to give special warnings to vehicles. A device with this kind of capability that can be coupled with a powerful and precise proximity detection system can be used in a great variety of ways, simply by making adjustment of the software that are appropriate for the specific need. A crucial consideration is that DEMs can be added to a facility to improve safety and improve operations without adding other infrastructure since they work in cooperation with PDSCs that will typically have already been integrated into vehicles such as fork lifts. 
     Turning now to  FIGS.  10 - 11 A , DEMs  201  can be applied to improve material handling operations in numerous ways other than for loading docks by making software changes and/or minor hardware adjustments. For example, the circuit board  1121  (the components of which are substantially described with respect to PCBA  221  ( FIG.  2   )) can be oriented in order to produce separated pulsed magnetic fields that are directed horizontally across the roadway. This may be simply accomplished in the illustrated embodiment by sliding the circuit board into a square housing  223  in a horizontal orientation as shown in  FIG.  11 A , rather in a vertical orientation as described above with respect to the portal area. And by orienting the DEM ferrites  204 ,  210 , described earlier, on the circuit board  1121  such that they are directed across the roadway, the direction and speed of vehicles traveling along the roadway can be measured. Of course, the very presence of the vehicles can be important for traffic control analysis and other reasons. This information can be used to alert the operator of the vehicle to potential dangers and/or threats to pedestrians and/or can take immediate actions to slow or stop the vehicles. Information acquired from interactions between DEMs and PDSCs and PADs can be automatically transmitted to the cloud where dashboards can be used to monitor and evaluate the movements of individual vehicles, groups of vehicles, and PADs for a variety of reasons. 
       FIG.  10    depicts a materials handling environment  1000  which includes a roadway  1001  and a fork truck  1003  that is moving material along the roadway  1001  toward a curve  1002 . A DEM  201  has been positioned along the roadway  1001 , at approximately the same elevation as the PDSC  1004  on the fork truck  1003 . The DEM  201  is positioned with the ferrites  204 ,  210  directed in direction A across the roadway  1001 . These ferrites  204 ,  210  produce the pulsed magnetic fields  1005 ,  1006 . 
     As the fork truck  1003  approaches the magnetic fields  1005 ,  1006 , the sensing ferrite  214  detects the semi-random PINGS from the PDSC  1004 . Receipt of these PINGs by the ferrite  214  results in activating the microprocessor  206  to take the actions required to accurately acquire signals. Similar to the explanation given for the DAC system described earlier, the UHF receiver  219 , by control of the microprocessor  206 , checks to determine if there is another transmitter in the area already using the selected frequency, such as 916 MHz. If that frequency is in use, the UHF transceiver will switch to an alternate frequency, such as 918 MHz, and begin transmitting a carrier signal that alerts any other DEMS or PDSCs in the area that this device is going to use this frequency for the next few milliseconds. If the first frequency is clear, the UHF transceiver  219  will use that frequency, 916 MHz in this example. 
     In the illustrated example, after starting UHF transmissions, the microprocessor  206  will immediately begin issuing pulsed magnetic fields  1005 ,  1006  from the ferrites  204 ,  210  at approximately 100 pulse-pairs per second. When the PDSC  1004  on fork truck  1003  reaches the first field  1005 , produced by ferrite  204 , which is shown as point  1007 , it will initiate the measuring process, until it reaches the field  1006  at point  1008 . After the fork truck  1003  exits the fields  1005 ,  1006 , the pulsing would end and the system would be ready for arrival of the next truck. In the event a fork truck might stop while in the fields, the pulsing would be ended after five seconds to avoid overheating of the ferrites. 
     Fundamental to being able to measure the speed and direction of travel of the fork truck  1003  is the physical arrangement and spacing of the ferrites  204 ,  210  and the timing of the pulsed magnetic fields  1005 , 1006 .  FIG.  11    shows a typical DEM assembly  1100 , which is constructed in the same way as DEM  201 , that includes a PCBA  221  in a housing  223 , and supporting elements  1101 , 1002 . The PCBA  221  may actually be two or three separate PCBAs that are wired together, depending upon the length of the housing  223 . The housing  223  would typically be supported by an angle  1101 , which, in turn, would be held in position by a support rod  1102 . This rod  1102  would be attached to any available structure above the DEM  1100 . With the rod  1102  being vertical, the PCBA  221  would be horizontal. With the ferrites  204 ,  210 , mounted as shown, the fields  1005 ,  1006  are directed horizontally, across the roadway  1001 . 
     Spacing  1120  between the ferrites  204 ,  210  and the pulse rate can be changed to satisfy performance requirements for the application being addressed. Spacing  1120  of the ferrites  204 ,  210  to each other in DEM  1000  shown in  FIG.  10    has been selected to be 36 inches. DEM  1000  is constructed in the same way as DEM  201 . Spacing  1122  and  1124  of the ferrites  204 ,  210  to ferrite  214  in DEM  1000  shown in  FIG.  10    has been selected to be 18 inches, with ferrite  214  positioned midway between the ferrites  204 ,  210 . The field  1005 ,  1006  pulse rate is chosen to be 100 pulse-pairs per second. This arrangement provides a speed resolution of approximately plus or minus five percent (+/−5%). If the need is to only determine if the fork truck  1003  is moving “slow” or “fast”, the separation can be reduced or the pulse rate can be reduced, or both.  FIG.  10    shows that there are two other useful points  1009 ,  1010  that can be used to measure speed a second time, if desired. It is also possible to further improve accuracy by using the strength of the magnetic fields  1005 ,  1006  between the detection points  1004 ,  1005 ,  1009 ,  1010 , such as explained above. 
     Fork trucks are known to overturn, on occasion, when making sharp turns, often as a result of excessive speed and/or of the load on the forks shifting. Also, payloads sometimes slide off the forks, striking pedestrians or striking other objects that the crush someone behind the object. Training, signs, and various safety techniques are sometimes used to encourage operators to properly reduce speed before making turns. By placing a DEM  201  prior to the entrance of a curve, as shown in  FIG.  10   , the speed of the fork truck  1003  can be determined and the PDSC system  1104  on the fork truck  1003  can either produce visual and audible warnings or send signals to the fork truck to command a slower speed. Managers, safety engineers or traffic planners can use a dashboard to monitor the speeds of the fork truck  1003  each time it enters and exits the curve, be alerted to speeds exceeding speed limit signs and/or training, and compare the operating habits of all operators for all fork trucks entering the curve  1002 . 
     A Proximity Detection System that is precise, can easily communicate proximity events to the cloud, and perform many specialized functions by simply adding one or more low cost DEMs, illustrates the value of having such devices within material handling facilities. Another indication of the operational value of being able to add DEMs to a facility that has been outfitted with an effective use of pulsed magnetic fields is the challenging control of traffic at intersections and of being able to report such activities. The functionality possibilities of using DEMs can be indicated by considering a four-way intersection such as depicted in  FIG.  12   . The details of the DEM functionality are the same as described in previous paragraphs. The DEMs reveal presence of vehicles, and measure and report their speed, and direction of travel. They can also detect the presence of PADs. However, for complex circumstances such as intersections, there must be a higher-level logic and there can be many versions. For example, there can be a rule that the first vehicle or pedestrian to arrive at a specific point, are given priority for entering the intersection. Alternatively, some directions may be given priority over others. To accomplish such a logic, there must be an administrator or controller. In the instance depicted in  FIG.  12   , PDSC controller  1221  is suspended above the center of the intersection  1200  performs that function. It may make decisions to produce signals to operators or may inhibit the movement of a vehicle into the intersection until the set priorities have been satisfied. The truck  1203  located in roadway  1202 , having a PDSC  1204  would be under the control of the PDSC  1221  in some preferred fashion. Likewise, truck  1209  in roadway  1208 , having a PDSC  1210  would also be subject to the control of the same PDSC  1221 . The primary information feeding into the PDSC  1221  would be derived from the DEMs  1205  and  1211  which produce the fields  1206 ,  1207 ,  1212 ,  1213 . Any other trucks entering from roadway  1201  or  1220  would be controlled by the logical management of the signals from the fields  1215 ,  1216 ,  1218 ,  1219  which would be generated by DEMs  1214 , and  1217 , along with the inputs from all the above. DEMs  1205 ,  1211 ,  1214 ,  1217  are constructed in the same way as DEM  201 . Although the management of all this information, according to the established logic for the facility involved, is not a sophisticated process, the possibilities are almost limitless. But, to produce a precise and safe intersection control, and to be able to report all events at the intersection to a dashboard is a significant achievement. When this can be accomplished by adding a relatively small amount of equipment (four DEMs and one PDSC controller) to be used in conjunction with an existing Proximity Detection System, the benefits-to-cost is significant. 
     If there is a need to investigate the traffic experiences at a particular location where there have been speeding complaints or accidents or near misses, a DEM can be equipped with a battery to allow it to be moved between locations without notice. There are many types of locations where speed monitoring and/or speed control is needed, along with accurate reporting. By installing a few DEMs at strategic locations in a facility, many types of traffic studies and operational practices can be performed. Whether fixed or moveable, the DEMs report the presence of passage, speed, direction to the cloud, allowing numerous types of evaluations to be made. The transient time of any or all vehicles between any selected points can be known and can be processed in various ways by use of the dashboard to evaluate various aspects of the facility traffic control and operator habits and practices. 
     The embodiments of the disclosure and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and examples that are described and/or illustrated in the accompanying drawings and detailed in the description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and features of one embodiment may be employed with other embodiments as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the embodiments of the disclosure. The examples used herein are intended merely to facilitate an understanding of ways in which the disclosure may be practiced and to further enable those of skill in the art to practice the embodiments of the disclosure.