Getting Cycle Times ©2009 Dr. B C Paul Note – These slides contain material from slides dating back to 2000 and also contains screen shots from the program FPC developed by Caterpillar Equipment Company

What We Have l We have a draft fleet of equipment, a production target, and haul routes. We still planned a lot about loading and fill factors the program does not know about l With this information we will be able to figure out how much material our fleet can really move

Pick The Select Tab Is anyone Noticing that We are Working From left to Right across The tabs? Click to select what combination we want to check

Lets Look at the Biggest Truck on Our Main Route Click to Production and Cost.

Note That Production and Cost has a Whole Set of Sub-tabs We want to work on cycle times (ie – how long does it take for The truck to make one complete material delivery trip – right now Everything is based on our guestimate)

The Program Starts Out Refusing to Tell Us Anything It’s on strike until we tell it how long It will take for our truck to back in And dump.

Where Could We Get That The Cat handbook has information on Typical times for maneuvers We can also do our own time Studies of trucks doing Similar things at our own or Other operations. Since I’m going to be backing Into a relatively small gyratory Crusher dump with a big truck I’ll go for the full 1.2 minutes

Our First Time Estimate Comes In Right now its telling me I have A huge wait time to get the Truck loaded (although by 30 minute guess Is not looking too bad if I Don’t break my arm patting Myself on the back)

The Initial Time Estimate is Usually A Mess The program tries to estimate the Loading cycle time – and when It comes to integer passes and Fill factors its usually quite Pathetic – fortunately we already Know what’s going on with that.

Adjusting for Something Realistic Start by putting in an integer number Of passes (we already estimated What to guess in earlier slides) Then adjust the fill factor till we get 100% of volume or payload without Exceeding 100% on the other parameter

Check for Adjustments That 81.5% fill factor is so low I’m Going to see if I can pull-off a 7 pass load

Yup – I Did It! That 30 minute guess looks real good

Interpreting the Screens FPC assumes single truck loading First the loaded truck pulls away and the empty Truck backs into its place – this hauler exchange Time is 0.7 minutes While the trucks are backing the loader is Scooping up material so by the time the truck is There the loader has a scoop of material to Discharge – discharging the bucket takes only 0.05 minutes The loader then makes 6 more passes at 0.48 Minutes per pass.

That of Course Brings Up the Fact that the 789 could only be loaded by Drive-By In drive by loading there is no backing – One truck pulls away and the next one Just pulls forward. The hauler exchange Time is greatly reduced. Because a drive by truck is less ideally Spotted that loader normally must swing A wider circle to load it. This takes time. (Earlier editions of the Cat handbook Estimate about 1.2 times longer cycles)

My Adjustments Adding about 20% to my loader cycle Time brings it up to about 0.58 minutes Per material pass My exchange time and first bucket time Must not be less than the loader cycle Time – if my truck zapped into place in 0 seconds flat the loader cycle would Just take longer for the first pass.

Now Lets Analyze My Haul Cycle 4.06 minute loading is close to The 4 minutes I guestamated This loader wait time is crumby I’m waiting minutes

What To Do About That Wait Time l My ratio of trucks to loaders was based on a 30 minute truck cycle and a 4 minute load cycle 8 trucks to a loader l Problem is my trucks could do 22.5 minute cycle so they are having to wait because the number of loaders is limited This situation is called “Over trucked” – there are too darn many trucks for each loader

Lets Do One of Those Engineering Refinements l 22.4 minutes / 4.06 minutes = 5.5 trucks per loader l I based my production on a number of trucks needed – I’ll keep the truck number and adjust the loaders 109 trucks / 5.5 = 19.8 loaders l I don’t know what 8/10ths of a loader looks like and I think I’ll keep it that way – 20 loaders

Jump Back to the Fleet Input Screen Change the number Of loaders to 20 Now Back to the Production and Cost Tab to Check on My Cycle

That Took a Bite Out of the Wait Time But Wait – How can my trucks Be waiting. With that last Adjustment I now have extra Loading capacity – ie – I am “Under Trucked”

A Bunch of Curses l Ever noticed how trucks on the interstate tend to move in groups? Not every truck follows an evenly spaced cycle and not every truck takes exactly the same amount of time Slow trucks bunch faster trucks behind them (just like many of you have cursed Grandmas and farm equipment when your in a hurry and they snarl traffic) Remember that “passing allowed” check-off box on your haul routes – this determines how bad bunching is l Your trucks are waiting on average even though you are “under trucked” because your trucks arrive in groups

How to Deal With Bunching l Can run full scale computer simulation where the computer tracks each simulated truck as an entity. – (that’s beyond anything in this course although Dr. Harpalani will give you some in Statistics, Probability and OR) l Caterpillar ran extensive simulations and time studies and built standard factor tables into their program You control what the program does by whether you allow passing on road segments And with

Your Pick for Bunching Conditions The default is average, Suppose I picked None (in practice I would Practically have to have Total computer control Of the system)

No Bunching – No Wait Time

Reducing Bunching l The traditional way of truck dispatching is to assign each truck to a particular shovel each day If a loader piles up – it piles up l Truck dispatching systems are an attempt to reduce this Have a truck dispatcher monitor the wait time on each loader and then send trucks to the loader that can service them for the quickest turn around from where they are Still have non-uniform drivers

Driver-Less Trucks l Not all operators coax performance from equipment equally l With 109 trucks that’s a heck of a lot of truck drivers I’m hiring l These things suggest the idea of replacing drivers with computer systems

How it Works l Put GPS devices into trucks and program the road network into memory Have a program steer the truck, control the acceleration and direct to a particular loader (not trivial software engineering) l Include radar and thermal analyzers to check for obstructions in the road Big cold objects in the roads are boulders Warm moving objects are workers and foreman Currently no way to match personal heat signatures to decide whether to run them down

Are We About to Dump Drivers and Bunching? l No l Driverless trucks can’t really reason their way around an obstruction when they find it l You better have good GPS signals that are not shadowed out in a pit at any hour of the day l Opportunities to deploy the technology are still a limited niche l I’m going back to Average Bunching for my Truck and loader study

This Does Bring Up a Question l How Did the Cat Program know it would take minutes to make a loaded trip to the Oil Shale Refinery l And 6.47 Minutes for an empty return

The Program Knows About the Performance Curves for Each Truck l Before programs (or when programs can’t handle the twist we want) Engineers used those curves to figure peak speed l They then multiplied those peak speeds by speed factors to adjust to average speed l With an average speed and distance you have a moving cycle time (Remember the formula Distance(ft)/(Speed(mph)*88) = time in minutes)

Peak Speed Established by Gradability Chart Read Down the Grade Line To the Intersection With the Weight Line Read Over to Gear Curve Read Down to the Speed Speed is 40 mph in 7th Gear (Note Gradability charts don’t work Down hill)

Enter the Retarder Chart (No I didn’t Say Retarded) Read Down the Net Favorable Grade to the Truck Weight Line Read Over to Gear Curve Read Down to the Speed Conclude 40 mph in 7th Gear

Old And New Methods l Once peek speed was established Old method used tables of speed factors (like in the Old SME Surface Mining Book) Caterpillar uses torque curves and operator efficiency assumptions to predict how fast the truck will reach peek speed and thus get an average speed

Checking for Tire Heating ©2009 Dr B C Paul Note – These slides contain material from slides dating back to 2000 and also contains screen shots from the program FPC developed by Caterpillar Equipment Company

Haul Trucks are Very Large l Tires flex and can get hot as a result of working under load l To avoid tire blow-outs we use Ton Miles Per Hour – TMPH l Each tire has a rating l You get the average load * average speed and compare to the TMPH rating