Can you increase efficiency and throughput by slowing down?

I recently had a discussion with a customer and an engineering firm about increasing throughput by slowing down the rate of a labeler from 400/minute to 380/minute. They recorded an improvement in efficiency to justify the change.  I questioned the decision from a thruput standpoint and wanted to come up with a good way to determine if an increase in efficiency actually increased the thruput or not.

Is slower better?

Efficiency is calculated using the following formula:

MTBF / (MTBF + MTR)

MTR = Mean Time to Repair
MTBF = Mean Time Between Failure

A properly buffered line should have capacity to handle the longest MTR on the line. The difference in maximum rates should be such that the table can go from full to empty in less time than the MTBF. For example, if you have a line like this:

Your labeler must have a MTR of 3 minutes or less and an MTBF of 9.9 minutes or more, giving us a minimum labeler efficiency of 77%. So what if I decrease my max rate in an effort to improve efficiency?

My minimum required MTR is the same since I’m still filling the buffer at 330 bpm, but my minimum required MTBF is now 19.8 minutes. This gives us a way to measure whether the decrease in rate has affected throughput. My labeler efficiency must now remain above 87% (19.8 / (3+19.8)) to keep the filler running and maintain throughput.

As the labeler slows down, its efficiency must go up to maintain throughput for the packaging line.

The formula can even more simply be expressed like this:

e = (Fr / Lr)

Where e = the minimum efficiency needed to maintain throughput
Fr = the max rate of the constraint
Lr = the max rate of the machine in question

If I run the labeler at 400 bpm I need to maintain a labeler efficiency of 77%. If I run it at 380bpm, I must maintain an efficiency of 87%. So if slowing the max rate of the labeler resulted in improving the efficiency from under 77% to something over 87%, then yes it will have improved throughput. If they were already running above 77% prior to the rate change, then throughput will be unchanged. If efficiency is under 87% after the rate change, then throughput will decrease.

In practice you have to find the right balance between rate and efficiency. It may be tremendously more difficult to maintain 87% than 77%, due to inconsistent materials or operator error.

The Goal by Eli Goldratt

The Goal by Eli Goldratt: Classic novel about the theory of constraints. I didn’t understand my job until I read this book.

Getting Things Done by David Allen: Read this book if you want to complete projects that have been lingering for years and be productive despite everyday distractions. Can’t recommend it enough.

The Visual Display of Quantitative Information by Edward Tufte: There’s a science to making great charts and graphs and this is the textbook. If you make charts for your job, you absolutely have to read this. See our results.

Priceless by William Poundstone: Before switching to Computer Science I toyed with being an Economics major in college. It’s a fascinating science and helps explain many things in the world. This book helped me understand that when it comes to price, throw economics out the window because psychology is everything.

The Long Tail by Chris Anderson: 20th century mass market products were about producing hits. Distribution and production costs have sunk so low, it’s now about producing anything for anyone. Does this book apply to our business? The constant stream of custom quote requests says yes.

The Toyota Way by Jeffery Liker: The Toyota Production system changed world wide manufacturing and this is probably the best written example of what it is.

The Wisdom of Crowds by James Surowieki: Polls are almost always right and committees are usually wrong. This book explains why.

Rework by Jason Fried and David Heinemeier Hansson: A takedown of standard business practices and ideas for new companies.

Any suggestions?

So far Twitter has been a fun distraction during the show and has gotten us some free press as an early adopter. It will be interesting to see how it will be used during Pack Expo in Chicago this year.

The best social media mavens aren’t robots spouting their company press releases. They post about whatever interests them and occasionally comment on industry news and events. It should go without saying that their posts may not always represent the views of their respective companies, but I’ll say it anyway. Here are some great industry tweeters:

PMMI
The Packaging Diva
Jake Garvey, Garvey Corporation
Michael Senske, Pearson Packaging
Mike Collins, Federal Mfg Co.
Kate Putnam, Package Machinery Company
Steve Windham, Omron
Marc Ostertag, B&R Automation

My entire packaging list.

Traditionally, beverage bottlers lubricate their conveyors with soap and water systems to prevent bottles from tipping over and extend the life of their wearstrips. With an eye on cost savings and sustainability, bottlers have been replacing these systems with “dry” lubricants that perform the same function, saving a tremendous amount of water. Most dry lubricants used for bottling aren’t actually dry, but are highly concentrated and stay on the chain surface for long periods of time. All of them were pretty good, and most dry lubricants even outperform soap and water lubes by a significant margin.

We’ve done a side by side comparison of several commercially available dry lubes with an eye on two factors:

1. How much do they reduce the friction between the conveyor and the product?
2. How clean is the lubrication? How much build of gunk and dirt do we see over time?

We’ve ranked six dry lube brands by this criteria and here are the results.

Friction Reduction Ranking

1. ICC’s Dry Traxx
2. Johnson Diversey’s Dry Tech V
3. Hartness DCL
4. Drylube.co.uk
5. Ecolabs DryExx
6. SKF
7. No lube (control group)

Head to head lube test conveyor

Our testing methodology was simple.  We created a multi-lane conveyor that we could raise up on one side, which created an incline.  We slowly lifted one side of the conveyor and saw which of the products started sliding back first.   Here are some important notes we took from our comparison:

1. For this test we used PET beverage bottles.
2. PTFE based lubricants (ICC, Johnson Diversey, and Hartness) strongly outperformed the silicone based lubes in reducing the friction between conveyor chain and PET bottles
3. The conveyor chains used in the test were Rexnord Platinum Series (PS) 770.
4. The tests were conducted over 110 minutes of run time
5. 3ml of each lubrication was used on each chain.
6. Three separate tests were performed

Sanitation Ranking

1. Drylube.co.uk
2. Ecolabs DryExx
3. ICC’s Dry Traxx
4. Johnson Diversey’s Dry Tech V
5. Hartness DCL
6. SKF

When looking at sanitation issues, we looked for what the chain and product looked like after a few hours of run time.   Was there dust or dirt build up?  Did we see any waxy or gooey build up in the knuckles of the chain? Here are some notes we took from the cleanliness comparison.

1. Drylube.co.uk, EcoLabs, and ICC strongly outperformed the others in this category.
2. The EcoLabs and DryLube.co.uk lubrication may have completely dried off during the 110 minute test.

ICC's Dry Traxx RTU is our recommended dry lubrication

We hope this comparison helps your company make their decision about which lubrication is best for you.  Out of all the lubrications we’ve seen, we recommend ICC’s Dry Traxx RTU.  It’s the best balance of performance and cleanliness and it’s also rated H1 and H2 for food contact.

For additional questions about dry lube or for a quote on a dry lube application system for a new or existing conveyor system, contact us today. All we need to know is the number of lubrication points.

This formula converts products per minute (ppm) to feet per minute (fpm) for a simple conveyor:

d * r * 1.1 = c

d = Product diameter (ft)
r = Desired product rate (products per minute)
c = Conveyor speed (fpm)

The 1.1 modifier is to overcome a shallow angle in a side transfer from one conveyor to the next. This may be more or less depending on the angle and the type of the transfer.

This formula converts products per minute (ppm) to feet per minute (fpm) for Bi Flo Accumulation tables and Infinity Accumulation tables:

d * r * 1.5 = Bc
d * r * 1.25 = Ic

Bc = Bi Flo conveyor speed (fpm)
Ic = Infinity conveyor speed (fpm)

The modifiers (1.5 and 1.25) may vary depending on how steep the outfeed guides are, but these are the most common starting points.

Shaft mounted gear reducers. That's me on the right.

There are a lot more variables to consider when converting the speed of a conveyor to the Hertz on a VFD. You need to calculate the revolutions per minute of the drive shaft. Sometimes this is given on the faceplate of the gearmotor as “Out RPMs” or “Shaft RPMs.” If not, the gearbox will have a ratio on it (10:1, 20:1, 60:1, etc.) and the motor will list how many RPMs it makes at its standard voltage (typically 60Hz). The conveyor pitch is the length of each link in the modular belt that engages one tooth of the drive sprocket. If the gearbox is mounted right on the drive shaft, it is called a shaft mounted motor and there is only one point of reduction. If there is a drive chain between the gearbox and the conveyor drive shaft (base mounted motor), there is an additional point of gear reduction in the ratio of the drive and driven sprockets on the drive chain:

60 * ( s / ( (p * t * v) )) = h
m / g / b = v


s = Conveyor speed (fpm)
p = Conveyor chain pitch
t = Teeth of the conveyor drive sprocket
v = Conveyor drift shaft RPMs at 60Hz
h = Frequency of VFD at desired conveyor speed (Hz)
m = Motor RPMs at 60Hz
g = Gearbox ratio
b = Ratio of drive to driven sprockets on base mounted systems

Basemounted drive system. The motor is mounted underneath and the drive chain is covered by the rounded guard on the left.

For example:
Desired conveyor speed: 84fpm
Chain pitch: 1.5″
# of teeth on conveyor drive sprocket: 16
Motor RPMs at 60Hz: 1700
Gearbox ratio: 30:1
Drive sprocket for base mount: 20 teeth
Driven sprocket for base mount: 24 teeth

(84 / ( (1.5" / 12") * 16 * (1700 / 30 / (24/20) ) ) * 60 = 53.3 Hz

Variable Frequency Drives (VFDs) control the frequency of the power being sent to the motor. This allows a control system to change the conveyor speeds based on line conditions.

So to get REALLY crazy and go all the way from product rate to the frequency coming out of the VFD, we use this for an Infinity Accumulation table:
60 * ((d * 1.25) / ( (p * t * (m / g / b) ) )) = h

Bi Flo Accumulation table:
60 * ((d * 1.5) / ( (p * t * (m / g / b) ) )) = h

A puck system is used to move unstable products through a packaging line. They’re popular in the cosmetics and personal care industries and can be purchased from a number of vendors such as Advantage Puck. The pucks and the products are separated at the end of the line and the pucks must be conveyed and reintroduced back to the beginning. A puck system provides a unique challenge for our line analysis calculation because stoppages in the line affect the flow of pucks upstream and downstream simultaneously.

Let’s look at a simple example of three machines.

Three machines in a packaging line with a puck return system.

Like any normal packaging line, this line has a constraint. Machine A runs at 300 products per minute (ppm) and the line can’t go any faster than that. Machine B accepts products from Machine A and sends them to Machine C. Machine C performs some sort of operation on the product, removes the product from the puck, and returns the empty back back to Machine A. If any machine malfunctions, all other machines must also shut down. Normally we can add an accumulation to help protect the constraint from the downtimes on other machines like this:

We added an accumulation table between Machines A and B to improve throughput, but does it help?

Unfortunately, Machine A requires a steady stream of empty pucks from Machine C to run. Downtimes on Machines B and C interrupt this stream, so despite having an accumulator downstream to allow A to keep running, line production shuts down anyway.

Downtime on Machine C cuts off the flow of empty pucks to Machine A, shutting down the whole line.

The same thing happens for downtime on Machine B.

We solve this problem by placing a second buffer upstream from the constraint in the empty puck return conveyor.

A second accumulator primed with empty pucks will allow the constraint to keep running.

If we have downtime on B or C, the second accumulator that was pre-primed with empty pucks will start emptying out and the original accumulation table will start to fill up at a rate of 300ppm. If the malfunctions on B or C are corrected before these tables empty out or fill up, then no production has been lost and throughput has been increased.

If B or C malfunctions, the first accumulator starts to fill up and the second starts to empty out, but the important thing is that Machine A keeps going.

Some important notes and questions:

How big should the accumulation tables be?
Both tables should hold enough products to handle the longest average repair time of any non-constraint machine, plus the number of pucks in transit.

Do the tables have to be the same size?
If you have two tables, they must be the same size because they are emptying out and filling up at the same time.

Does the second accumulator have to be in the empty puck return section?
No, but for the majority of cases it is the best place. Otherwise you will have to remove all the empty pucks from the system at the end of a shift or allow empty pucks to pass through machines without products in them. It makes sense from throughput standpoint and an operations perspective to accumulate all the empty pucks on accumulator 2 at the end of the shift.

How many pucks should I put on the system?
Fill the accumulation table prior to Machine A with empty pucks and don’t put any more on. Adding more pucks will decrease the line’s throughput.

A plastic bag inside a paper bottle

“In principal, Ecologic is a bag-in-bottle with the consumer interface being almost identical to standard packaging,” says Julie Corbett, founder and CEO of Ecologic Brands, Inc. “The Ecologic bottle offers enhanced functionality [over bag-in-box formats] as it is easier to pour, hold and grip.”

The bottle is a biodegradable, paper-based, rigid container that houses a plastic bag inside. Once in a landfill the paper container breaks down quickly leaving the much smaller plastic bag. What I love about this packaging is that it addresses some of the concerns that bottlers and machinery manufacturers have had for years in that weaker and/or flexible packaging reduces the ability to fill, pack, and ship the products efficiently, requiring more overall energy usage on packaging lines. I haven’t seen any of these bottles yet in person, but if this trend continues I think it could eventually see widespread adoption.

We keep track of the queue levels at every operation in our facility. Here’s a good example of how we were able to reduce 12 charts down to three without losing any information.

Before

After

Big thanks to this nifty Excel AddIn for getting Sparklines to work properly.