Analysis of the articulated crane operating data can give an indication of how the crane has been used, and based on that, effective measures can then put in place for improvements.
Articulating pick and carry cranes are ubiquitous in Australia. Since their inception in 1980 they have proliferated in the thousands and have become a valued workhorse in many industries.
The name “pick and carry” suggests an indication of how these cranes are used and the utilitarian nature of the cranes. Thus, pick and carry cranes find themselves being used in a wide variety of applications, high frequency of use and with widely varying loads.
The articulating pick and carry crane has unique characteristics that differentiate it from slewing cranes and as a result a skilled slewing crane operator can unwittingly find himself in a potentially dangerous situation when using a pick and carry crane.
Most modern cranes are equipped with data loggers which store critical parameters relating to the crane’s use and rated capacity. Increasingly cranes are being equipped with remote monitoring systems, also known as telematics. Data log analysis has historically been used together with crane condition inspections as a means of investigating crane incidents after the fact. Routine data log analysis can identify potentially dangerous crane use and corrective measures then put in place before an incident occurs. However, there is a time-lapse between the incident and the analysis. Telematics provides near real-time data which can greatly shorten the time between the activity and corrective measures.
While data loggers and telematics systems can provide reams of data, the analysis of the data can be challenging.
Monitoring crane movements through data analysis can give an indication of the behaviour of the crane operator and whether a crane is being used within its designed load spectrum class. There are many common actions relating to pick and carry cranes which in themselves are not necessarily dangerous behaviours. Some of these are:
– Overload due to end of luff ram stroke reached;
– Operating outside a crane’s rated capacity;
– Exceeding a crane’s pick and carry maximum allowed speed;
– Articulating with the load near the rated capacity;
– Attempting high capacity lifts with significant side slope;
– Attempting lifts when crane is in travel mode;
– Driving with the boom not stowed properly;
– Parking the hook block against the boom tip.
On-board LMI systems provide many safety features in the form of warnings or motion limiters which if ignored or overridden can result in the crane being used outside the manufacturers safe use guidelines. It may not be possible to analyse a single event taken out of context of other crane parameters to determine if the operator was working in an unsafe manner.
Luffing ram end of stroke
Luffing rams on pick and carry cranes will eventually reach end of stroke if an operator continues luffing. Reaching the end of stroke will create a pressure spike in the luffing cylinder which the LMI could interpret as an overload if the pressure is high enough. This is often referred to as a “false overload”. It is straightforward for a person to look at the data pertaining to an end-of-stroke overload and quickly ascertain this to be a “false overload” due to zero load leading up to the overload and then the boom angle reaching 63 degrees concurrent with the overload spike however there can be tens of thousands of rows of data to sort through. This is an example where the overload event can be identified by a software application but flagged as end-of-stroke condition.
Use of override to increase capacity
It is common to lift a heavy load and have the LMI detect an overload. Accepted practice is to ground the load by hoisting down, then repositioning the crane to achieve a higher capacity and performing the lift again. However, this takes time, it is much easier to use override to decrease radius and thus increasing the rated capacity. The following is an example of a lift that went straight into overload, operator then used the override function to increase his capacity by increasing his boom angle.
Preparing the crane for road travel
When preparing a crane for travel it is imperative that any load is removed, and the boom stowed properly. Preparation must be done before switching the crane into a highway mode of operation. If the correct stowage and highway mode selection sequence is followed, then there shouldn’t be any cabin warnings or overload/override data log records generated. Some may believe following the incorrect sequence isn’t an issue, however it is imperative to understand that pick and carry load charts are valid only when the crane is configured for lifting operations.
Because pick and carry cranes don’t have outriggers the suspension must be locked so that it can achieve its rated capacity according to its load charts. If the crane suspension is unlocked, then there may not be a published load chart and lifting is prohibited. Data log records for a travel mode attempt with the boom not stowed is best viewed in tabular format. In the case below, the operator attempted to switch to Highway mode but due to the boom angle being above 10 degrees the LMI warned that Highway mode is inhibited and to stow the boom as evidenced by the Mode 2. The operator then switched back to crane mode (Mode 0), lowered the boom, then entered Highway mode successfully.
Data Log Analysis
Due to the large amounts of data available it is desirable to automatically determine whether there are events that require further investigation. Tools are available that will analyse weeks and months of data and summarise Overload, Override, Bridging, and Two-Blocking events. Data available will vary between manufacturers.
Crane utilisation is important not only from a commercial perspective but also as a safety issue so that a crane is not used outside its designed load spectrum. The load spectrum can be automatically generated from data log records with selectable thresholds.
Crane utilisation reports can be automatically generated from data log records. Utilisation reports can provide data which allows for educated decision making –
– Do we have the correct crane on the worksite?
– Is the crane being overworked?
– Is the Rated Capacity too low for the worksite?
– Alternatively, is the Rated Capacity more than it needs to be? Are we competitive?
Utilisation data is best presented in a graphical format which shows at a glance if the crane is under or over utilised both in regard to time performing lifting activity and rated capacity.
Because two-blocking the hook block is standard procedure for pick and carry cranes there can be hundreds of ATB events over a few weeks. The following crane example had 478 two-blocking events over a period of eight weeks, most of which were no-load two-blocking events indicating that the two-blocking was used to “park” the hook block against the boom tip. A few representative examples following the ATB History table.
Lift Related Data
The table above shows information on the lift data that can beautomatically generated.
Pick and carry cranes play a vital role in many industries and when used within manufactures guidelines can achieve a high level of safety. Routine review of crane use is important not only as a safe use monitoring tool but also for commercial application. Data log download and analysis can be useful but perhaps sometimes an impractical approach to crane use monitoring. There are drawbacks such as limited data logging memory in LMIs, labour intensive data download and analysis, machine down-time, and time lapse between events, analysis, and corrective actions. The table shows information on the lift data that can be automatically generated including:
– Reducing the time lapse between event and action from weeks to minutes;
– Data storage in months and years instead of days;
– Off-crane data storage independent of LMI data logs;
– Data available to multiple users via website log-in accounts;
– More data available due to far less database resource restrictions.
Note: Crane data analysis is a useful safe use monitoring tool which can also provide an indication of how much of a cranes-designed working period has been used per AS 2550.1-2011 cranes hoists and winches – safe use – general requirements. DWP data log review is not a replacement for a major assessment by a competent engineer but it can provide an estimation in near real time of remaining time before a major assessment is required.
By CICA technical committee member, Jon Koval.