Transcript Trucks and Loaders - Supplemental Teaching Resources

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

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 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
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
The Cat handbook has information on
Typical times for maneuvers
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 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 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

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 would
Practically have to have
Total computer control
Of 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 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

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


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