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Expert Operator White Paper

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  • 1. Expert Operator Control for Increasing Safety, Productivity, and Operability of Cranes Dr. Khalid Sorensen CAMotion Cranes Inc. 554 North Avenue NW Atlanta, GA 30318 Phone - (404) 920-0735 Fax - (404) 920-0734 E-mail: khalid.sorensen@camotion.comKey words: Expert Operator, Crane Control, Anti-Sway, Crane Automation, Collision Avoidance, Crane Accidents, Crane Fatalities INTRODUCTIONCranes are critical components of industrial productivity. This is especially true for the production of primary metals. Inmany industries, cranes are only used intermittently (e.g. for maintenance or machine setup). In contrast, companies thatproduce iron, steel, and other primary metals utilize cranes continuously as a principal means of material handling 1 . Anincreasing awareness is developing among those who use heavy duty cranes that improving crane safety and productivity isof paramount importance 2 .The degree of crane safety and productivity at a given facility can largely be attributed to the crane operators. The skillwith which operators are able to drive a crane directly affects load swing, collisions, efficiency, crane maintenance, and thegeneral safety of plant personnel.While most would concede that skilled crane operators are essential for maintaining safe and efficient production, in practice,untrained and novice operators often perform many of the crane manipulation tasks. In the case of floor controlled cranes,“virtually everyone on the production floor will at one time or another operate the crane 3 .”Even among those who have undergone formal crane training, studies have shown that approximately 80% of crane breakdownsare due to operator errors 2 . This result is partly due to the fact that crane operators have a lot of things on which they mustsimultaneously concentrate 3 . These include controlling load swing, load positioning, avoiding collisions with both fixed andmoving obstacles, walking through the workspace, communicating with coworkers, and correctly actuating the pendent/radiobuttons, to name a few. A laps in concentration, or a developed sense of complacency with regard to any one of these taskscan have unfortunate results.In one facility, for example, cranes are used to facilitate the throughput of metal coils to and from cooling racks. Based oncompany-generated incident reports between 2000 and 2010, 101 collisions were reported involving the cranes that service theracks. 88 of those collisions were due to operator error. The cost associated with the collisions was very large, and includedthe cost of coil rework/scrapping, crane repair, rack repair, lost production, and operator injuries.In a study of OSHA inspection reports generated between 1997 and 2007, 248 crane incidents were examined 4 . Nearly half ofthese incidents occurred in the steel industry. The incidents resulted in 133 fatalities in addition to another 133 injuries. Theleading cause of a fatality or injury was when an individual was crushed by a load. It was estimated that 70% of the incidentsmight have been avoided had the crane personnel been operating in accordance with proper procedure and expertise. It isworth emphasizing that this study only examined incidents for which an OSHA report was generated; these represent onlya small fraction of global crane incidents, which may easily number in the thousands.
  • 2. The economic loss, personal injuries, and fatalities brought to light in these studies highlight an important point: the skillof the operator, and his or her diligence in adhering to training, is of paramount importance. Not only are expert craneoperators able to reduce down time and maintenance, but they also beneficially affect plant safety 3 .Given the importance of expert crane operation, this paper examines a recent technological development related to craneoperation called EXPERTOPERATORTM ( EOTM ). EOTM has a single function: to help crane operators of all skill levelsperform like expert crane operators, and, in so doing, enhance the safety and efficiency of crane operation.This paper describes EOTM , and presents data from industrial implementations of EOTM . Specifically, Section 1 describeshow EOTM is installed onto cranes, and its theory of operation. In Sections 2 through 5, data from industrial field trialsshow how EOTM affects load swing, positioning efficiency, collisions, and ease-of-use. DISCUSSION1 What is EXPERTOPERATORTM ?EOTM is a hardware module that helps operators of all skill levels drive a crane like an expert. This means that even novicecrane operators can reduce load swing, position loads more efficiently, avoid collisions, and reduce operator-error-inducedmaintenance requirements. EOTM works by intercepting pendent or radio-pendent commands. The intercepted commandsare converted into commands similar to those issued by expert crane operators. Then, the expert commands are issued tothe crane’s motor drives. This open-loop method for command modification is illustrated in Figure 1. Figure 1: EOTM Intercepts Pendent/Radio Commands.To understand how and why EOTM modifies commands, consider the following hypothetical scenarios in which an expertand novice crane operator attempt to stop a trolley from moving in the forward direction: • NOVICE. When the novice operator attempts to stop the trolley, he simply removes his finger from the trolley-forward button on the pendent. After doing so, the trolley quickly comes to a stop. However, because of the abrupt stop, the suspended load begins to swing. • EXPERT. When the expert operator attempts to stop the trolley, his experience dictates that he should not simply remove his finger from the trolley-forward button, as this would result in load swing. Instead, he skillfully presses and releases the button several times in order to finesse both the trolley and the suspended load to a safe stop without load swing.The key step that differentiates the experienced crane operator from the novice is the added extra button pushes. The extrabutton pushes were skillfully timed to control the trolley and the load to a safe stop. EOTM uses precisely the same strategyas in the hypothetical example to improve crane control: It subtly adds correctly-timed button pushes to all commandedmotion. This means that anytime an individual uses EOTM , it doesn’t matter whether he or she is a novice or experiencedoperator. The resulting motions of the crane will be as if an exceedingly skilled operator were driving.The practical result of EOTM , is that load swing is reduced while positioning efficiency is increased. Also, because the craneis easier to manipulate, collisions and near misses are significantly reduced.
  • 3. 2 Load SwingEOTM has been installed on industrial cranes across several industries, including primary metals, heavy equipment, andautomotive. In several cases, the operation of a given crane has been filmed in order to visually document its behavior. Sixsuch videos have been analyzed in order to quantify the effectiveness of EOTM at suppressing load swing1 .In each video, an operator manipulates a crane equipped with EOTM . Generally, the crane is accelerated to full speed, andpermitted to travel at full speed for several seconds. Then, the crane is brought to a stop by the operator, who releasesthe pendent/radio actuation button(s). In some cases, the operator causes the crane to travel in either the bridge or trolleydirection. In other cases, both the bridge and trolley are moved simultaneously. The amount of load sway exhibited by thecrane after the bridge and trolley have come to a stop was determined by post processing the videos.The results of this analysis are summarized in the charts of Figure 2. In addition to displaying how much load swing wasexhibited by each crane with and without EOTM . The charts also show the industry in which the crane is used, the crane’s 1 Some videos are available for public viewing, courtesy of end-users, at http://www.youtube.com/user/CAMotionRobotics.Industry: Primary Metals Load Swing (Manual): 6.87 ft. Industry: Primary Metals Load Swing (Manual): 2.46 ft.Capacity: 30-Ton Load Swing (EO): 0.39 ft. Capacity: 25-Ton Load Swing (EO): 0.42 ft.Use: Maintenance % Reduction: 94.3% Use: Material Handling % Reduction: 83.0%Industry: Primary Metals Load Swing (Manual): 1.51 ft. Industry: Heavy Equipment Load Swing (Manual): 1.48 ft.Capacity: 35-Ton Load Swing (EO): 0.18 ft. Capacity: 20-Ton Load Swing (EO): 0.06 ft.Use: Material Handling % Reduction: 88.0% Use: Assembly % Reduction: 95.6%Industry: Heavy Equipment Load Swing (Manual): 6.58 ft. Industry: Crane OEM Load Swing (Manual): 2.33 ft.Capacity: 20-Ton Load Swing (EO): 0.48 ft. Capacity: 20-Ton Load Swing (EO): 0.12 ft.Use: Production % Reduction: 92.7% Use: Shop Crane % Reduction: 94.8% Figure 2: Experimental Results of Load Swing Reduction from Different Industrial EOTM Installations.
  • 4. load capacity, and its primary function. These results indicate that EOTM is capable of reducing load swing by approximately90%. When EOTM was disabled, the average load swing exhibited by all the cranes was approximately 3.5 feet. Whereas,when EOTM was enabled, the average load swing was 3.3 inches.It should be noted that the loading conditions of each of the six cranes varied. In some loading configurations, large horizontalloads were suspended from the bottom block. In other cases, both short and long sections of rigging were used to suspendcompact loads. In one case, the crane remained unloaded. This is significant because it demonstrates that EOTM is effectiveunder a variety of loading configurations.3 Positioning EfficiencyIn addition to the industrial examples of EOTM discussed in the preceding section, this section presents six more industrialexamples of EOTM , this time in the context of positioning efficiency.In order to determine how EOTM affects positioning efficiency, videos were taken of operators during load positioning tasks.The load positioning tasks were repeated two times - once with EOTM enabled, and once with EOTM disabled.The specific manipulation task completed by each operator varied somewhat, depending on the application. In one application,large steel rolls were moved into holding racks. Another application involved the precise placement of large vehicle parts inmachining fixtures. In a third application, a counter weight was moved from one location on the shop floor to another, whileavoiding obstacles. A forth application required 15-ton coils to be moved from processing areas to a load staging area. Twoapplications involved manipulating the crane through an “obstacle course” as quickly as possible.Figure 3 shows hook motion for a typical positioning task, both with and without EOTM . This motion was captured byusing a laser measuring system, in conjunction with a camera that was attached to the trolley. The camera was oriented toface downward so that the bottom block and surrounding workspace was in the camera’s field of view. This figure providesa visual indication of the degree to which EOTM is capable of suppressing load swing. When EOTM is disabled, the loadoscillates substantially, whereas, when EOTM is enabled, the hook motion is smooth and well controlled. The oscillationsuppressing capabilities of EOTM may be a contributing factor to how EOTM reduces positioning time. 3 meters Manual EO START END Figure 3: Hook Motion for Typical Positioning Move, EOTM Enabled & Disabled.The time expended during each positioning task is summarized in the charts of Figure 4. These results indicate that EOTMreduced the time required for load positioning by at least 20%, and as much as 50% in one case. The average time reductionfor all cases was 34%. While some of this variance may be attributed to the nature of the different positioning tasks, the skilllevel of the different operators may also be a contributing factor.Because EOTM converts all commands into “expert” commands, the degree to which an operator already drives a crane “likean expert” affects the degree to which EOTM will improve his or her positioning efficiency. Therefore, a novice operator maybenefit much more from EOTM than a highly-skilled operator.
  • 5. Industry: Primary Metals Positioning Time (Manual): 88 s. Industry: Primary Metals Positioning Time (Manual): 40 s.Capacity: 30-Ton Positioning Time (EO): 50 s. Capacity: 35-Ton Positioning Time (EO): 20 s.Use: Maintenance Shop % Reduction: 43% Use: Roll Shop % Reduction: 50%Industry: Heavy Equipment Positioning Time (Manual): 198 s. Industry: Crane OEM Positioning Time (Manual): 116 s.Capacity: 60-Ton Positioning Time (EO): 137 s. Capacity: 40-Ton Positioning Time (EO): 66 s.Use: Production % Reduction: 31% Use: Shop Crane % Reduction: 43%Industry: Crane OEM Positioning Time (Manual): 49 s. Industry: Cable Positioning Time (Manual): 112 s.Capacity: 5-Ton Positioning Time (EO): 36 s. Capacity: 20-Ton Positioning Time (EO): 89 s.Use: Shop Crane % Reduction: 27% Use: Coil Handling % Reduction: 20% Figure 4: Experimental Results of Load Positioning Times from Different Industrial EOTM Installations.4 CollisionsAlthough EOTM is an open-loop crane control technology that does not use any obstacle-detecting sensors, it does havean effect on the frequency of collisions. To substantiate this assertion, this section presents data from a study conductedthrough a collaboration between CAMotion, the Georgia Institute of Technology (Georgia Tech), and an end-user in theaircraft manufacturing industry.The study investigated how EOTM technology affects collisions and near misses. To this end, close-tolerance crane manip-ulation tasks were completed by several crane operators. Each operator completed the manipulation tasks multiple times.Sometimes EOTM was enabled. Other times EOTM was disabled.While a given operator was completing the manipulation tasks, an observer noted the number of collisions or near missesthat occurred. A data recording device developed by Georgia Tech was affixed to the pendent. This device recorded themove times, as well as the number of times the operator depressed the various pendent buttons (i.e. north-south, east-west,up-down). After operators completed the study, they were asked to provide candid feedback about how the technologyaffected their ability to operate the crane.
  • 6. Table 1 summarizes the results of five operators who participated in the study. Their skill level varied from novice to expert.For operators A, B, C, and D, EOTM significantly reduced the number of collisions or near misses from an average of 9.2incidents per trial to 0.5 incidents per trial. In the case of operator E, the technology had no effect on collisions because thisoperator did not experience any collisions with or without the technology. Table 1: Experimental Results from Operator Study in the Aircraft Manufacturing Industry Collisions or Pendent Button Press/Release Count Operator Experience Operator Comments Trial EOTM Move Time Enabled Near Misses (mm:ss) Up Down East West North South Total 1 No 4 07:11 3 4 30 46 47 21 151 A Moderate "Its great, made it a lot easier." 2 No 9 05:21 1 1 32 39 48 12 133 3 Yes 0 06:30 2 2 4 4 21 3 36 "It was easier to anticipate 1 No 12 05:50 2 3 24 24 50 36 139 B Novice stopping." 2 Yes 0 04:36 1 1 3 5 9 6 25 "Incredible, quickly builds 1 No 7 06:59 1 2 8 16 19 11 57 C Expert confidence." 2 Yes 0 03:31 2 2 5 3 6 3 21 1 No 14 07:37 1 1 27 33 24 28 114 D Novice "It felt much safer." 2 Yes 2 04:28 1 1 10 5 13 13 43 1 No 0 05:45 1 1 9 27 31 22 91 "The stopping distance remains, just limited swing when 2 Yes 0 04:25 1 1 2 8 15 10 37 E Moderate reached. Less stress to 3 No 0 03:21 1 1 7 12 20 18 59 constantly monitor the load." 4 Yes 0 03:15 1 2 4 12 8 10 37The portion of the data concerned with move time affirms the results reported previously in Section 3. On average, trialswere completed in approximately 6 minutes when EOTM was disabled. When EOTM was enabled, trials were completed inapproximately 4 minutes and 30 seconds. This represents a 25% improvement in efficiency.5 Crane Ease-of-UseA given technology may beneficially affect load swing, positioning efficiency, and the frequency with which collisions occur.However, if these benefits are gained at the expense of increasing the difficulty operators experience while driving the crane,the benefit of the technology is marginalized. The post-experiment comments provided by the operators in the previousstudy suggest that EOTM simplifies crane operation. To further substantiate this notion, this section considers a seeminglyunrelated result from the previous study: the pendent button press/release count.It can be noted from Table 1 that operators pressed pendent buttons much more frequently when EOTM was disabled thanwhen EOTM was enabled. On average, a given operator pressed pendent buttons 106 times to complete a manipulationtask when EOTM was disabled. When EOTM was enabled, the average number of button presses was reduced to 33. Tounderstand why this is significant, some background information is warranted.When an operator attempts to move a load, he or she mentally accomplishes several steps. First, the operator synthesizesa desired trajectory along which to move the load. The desired trajectory is then decoupled into the kinematic componentscorresponding to the different modes of actuation (i.e. north-south, ease-west, up-down). The decoupled trajectories arementally mapped to the corresponding pendent buttons. Finally, the operator attempts to physically actuate the correctcombination and sequencing of pendent buttons. As the crane begins to move through the workspace, the operator continuallymakes command adjustments so that the load follows the desired path. In this way, the operator acts like a control elementin a feedback loop.This type of in-the-loop interaction contributes most significantly toward performance differences between novice and expertoperators 5 . Highly skilled operators have a very refined in-the-loop operational ability, whereas novice operators lack skill inthis area.Ordinarily, a high level of in-the-loop skill is warranted because the dynamics of a crane are difficult to control. Frequentcommand-adjustments (i.e. frequent button pushes) are necessary to combat load swing. In contrast, cranes equipped withEOTM exhibit dynamics of a different sort. The load swing is mitigated by the technology and not the operator. In this way,
  • 7. the operator need only control the rigid-body position of the load, and not the swing of the load. In this simplified dynamicsituation, a high degree of in-the-loop skill is not required because the crane is easier to control. Consequently, less frequentcommand-adjustments (i.e. button pushes) are necessary. Simply stated, few button pushes are evidence of a system that iseasy to control. Many button pushes suggest that a system is difficult to control.In light of the preceding, the pendent button press/release results of Section 4, provide a quantitative metric to substantiatethe effect that EOTM has on crane operability. Namely, that cranes equipped with EOTM are easier for operators to drive. SUMMARYSkilled crane operators significantly contribute to plant safety and efficiency. This is especially true in iron, steel, and otherprimary metals industries where cranes are a principal means of material handling. Given the importance of skilled craneoperators, a crane control technology has been developed called EXPERTOPERATORTM ( EOTM ) that helps individuals of allskill levels perform like expert crane operators. Numerous industrial installations of EOTM were studied to determine theeffects that this technology has on load swing, positioning efficiency, collisions, and crane operability. Experimental resultsdemonstrated that EOTM reduced load swing by approximately 90%. When using EOTM , operators were able to positionloads roughly 30% more quickly than when the technology was disabled. The technology also helped operators reduce thenumber of collisions and/or near misses occurring during some precise positioning moves. Finally, an analysis of pendentbutton pushes suggested that EOTM simplifies the dynamics behavior of cranes, thus, making them easier for operators tocontrol. ACKNOWLEDGEMENTSThe author would like to thank Dr. William Singhose from the Georgia Institute of Technology for technical discussions thatassisted in the completion of this study. A debt of gratitude is also extended to Kelvin Peng from the Georgia Institute ofTechnology, and Will James and Pat Barber from CAMotion for their engineering and system installation expertise.REFERENCES1. J. Rowe, “Smart Crane Control - Improving Productivity, Safety and Traceability,” AISTech, vol. 2, pp. 1341–1346, 2011.2. I. L. A. Horst, “Modern Crane Works Safety Technology,” AISTech, vol. 2, pp. 1355–1366, 2011.3. R. Geddes, “Training Crane Operators to their Crane Drive Systems,” AISTech, vol. 2, pp. 1117–1122, 2009.4. P. Doyle, “Crane Accidents and Fatalities,” AIST 18th Annual Crane Symposium, 2011.5. M. Fujita, M. Kamata, and K. Miyata, “Clarification of Cognitive Skill in Mechanical Work and Its Application,” Int. J. of Human-Computer Interaction, vol. 18, no. 1, pp. 105–124, 2005.