Getting Cycle Times

©2009 Dr. B C PaulNote – 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

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 With this information we will be able to

figure out how much material our fleet can really move

Pick The Select Tab

Is anyoneNoticing thatWe areWorkingFrom left toRight acrossThe 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 forThe truck to make one complete material delivery trip – right nowEverything is based on our guestimate)

The Program Starts Out Refusing to Tell Us Anything

It’s on strike until we tell it how longIt will take for our truck to back inAnd dump.

Where Could We Get That

The Cat handbook has information onTypical times for maneuvers

We can also do our own timeStudies of trucks doingSimilar things at our own orOther operations.

Since I’m going to be backingInto a relatively small gyratoryCrusher dump with a big truckI’ll go for the full 1.2 minutes

Our First Time Estimate Comes In

Right now its telling me I haveA huge wait time to get theTruck loaded(although by 30 minute guessIs not looking too bad if IDon’t break my arm pattingMyself on the back)

The Initial Time Estimate is Usually A Mess

The program tries to estimate theLoading cycle time – and whenIt comes to integer passes andFill factors its usually quitePathetic – fortunately we alreadyKnow what’s going on with that.

Adjusting for Something Realistic

Start by putting in an integer numberOf passes (we already estimatedWhat to guess in earlier slides)

Then adjust the fill factor till we get100% of volume or payload withoutExceeding 100% on the other parameter

Check for Adjustments

That 81.5% fill factor is so low I’mGoing to see if I can pull-off a 7 passload

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 emptyTruck backs into its place – this hauler exchangeTime is 0.7 minutes

While the trucks are backing the loader isScooping up material so by the time the truck isThere the loader has a scoop of material toDischarge – discharging the bucket takes only0.05 minutes

The loader then makes 6 more passes at 0.48Minutes 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 oneJust pulls forward. The hauler exchangeTime is greatly reduced.

Because a drive by truck is less ideallySpotted that loader normally must swingA wider circle to load it. This takes time.(Earlier editions of the Cat handbookEstimate about 1.2 times longer cycles)

My Adjustments

Adding about 20% to my loader cycleTime brings it up to about 0.58 minutesPer material pass

My exchange time and first bucket timeMust not be less than the loader cycleTime – if my truck zapped into place in0 seconds flat the loader cycle wouldJust take longer for the first pass.

Now Lets Analyze My Haul Cycle

4.06 minute loading is close toThe 4 minutes I guestamated

This loader wait time is crumbyI’m waiting 10.18 minutes

What To Do About That Wait Time

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

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

22.4 minutes / 4.06 minutes = 5.5 trucks per loader

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

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 numberOf loaders to 20

Now Back to theProduction and CostTab to Check onMy Cycle

That Took a Bite Out of the Wait Time

But Wait – How can my trucksBe waiting. With that lastAdjustment I now have extraLoading capacity – ie – I am“Under Trucked”

A Bunch of Curses

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

Your trucks are waiting on average even though you are “under trucked” because your trucks arrive in groups

How to Deal With Bunching

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)

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 wouldPractically have to haveTotal computer controlOf the system)

No Bunching – No Wait Time

Reducing Bunching

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

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

Not all operators coax performance from equipment equally

With 109 trucks that’s a heck of a lot of truck drivers I’m hiring

These things suggest the idea of replacing drivers with computer systems

How it Works

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)

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?

No Driverless trucks can’t really reason their way

around an obstruction when they find it You better have good GPS signals that are not

shadowed out in a pit at any hour of the day Opportunities to deploy the technology are still

a limited niche I’m going back to Average Bunching for my

Truck and loader study

This Does Bring Up a Question

How Did the Cat Program know it would take 10.64 minutes to make a loaded trip to the Oil Shale Refinery

And 6.47 Minutes for an empty return

The Program Knows About the Performance Curves for

Each Truck Before programs (or when programs

can’t handle the twist we want) Engineers used those curves to figure peak speed

They then multiplied those peak speeds by speed factors to adjust to average speed

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 LineTo the Intersection With theWeight Line

Read Over to Gear Curve

Read Down to the Speed

Speed is 40 mph in 7thGear

(Note Gradability charts don’t workDown hill)

Enter the Retarder Chart (No I didn’t Say Retarded)

Read Down the Net FavorableGrade 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

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 PaulNote – 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

Tires flex and can get hot as a result of working under load

To avoid tire blow-outs we use• Ton Miles Per Hour – TMPH

Each tire has a rating You get the average load *

average speed and compare to the TMPH rating