Getting Started with Stops

I recently had a former co-worker stop by my office with a question.  He had transferred away to a new assignment at another factory in our company.  His new factory had a lot of older equipment, mostly hard-wired control and very little communication capability with the control systems.  The plant had started using a Line Event Data System to gather data about production, but since there was no communication to the equipment, all data was being input by operators.  The operators weren’t very accurate in writing all events down or in how they timed what happened, so the resulting data was of little use.  My co-worker’s question was, “What would I do first to collect data from this equipment, given a small budget and low technical skills to install anything at the site?”

 My co-worker explained that the food line in question was a large jar packing line with many operations involved.  The jars were depalletized, cleaned, filled, pasteurized, labeled, packed into cases, and palletized.  There was a lot of accumulation conveyor between the operations as well.  He thought that maybe installing a photo-eye on the either side of the filler would be a good place to start.

 “Well,” I said, “the filler is probably a good place to start, as that is likely the constraint of the line.  Is that correct?”  He explained that yes, the filler was the critical operation of the line and that the rest of the line was set up to keep it fed and to take away filled jars fast enough to avoid shutting down the filler.  Most lines have a constraint, or bottleneck, generally the most complex and expensive part of the line, and if designed right, the slowest.  In the simplest of logic, you can assume that if the constraint is stopped, the line is down, as the time down cannot be made up.  Other parts of the line can go up and down, but as long as the constraint is not impacted, the line is still producing product.

 “Now,” I continued, “tell me how you want to use photo eyes to collect data.”  He explained that if there were jars passing by, then the filler was running.  I told him that with the right logic, that would be true, and that an additional benefit would be that if the photo eye sensor were put in the right place where there was always a gap between products, an accurate count could be made of product, which could be used to determine rates.  For this to work, though, the sensor would have to be connected in some way to communicate to the software tracking stops and counts.  Typically, this is done by wiring the sensor to an input of a Programmable Logic Controller (PLC).  Then the PLC can programmed to recognize the significance of the sensor being blocked to count each blocked condition as a product made, to time the period between products to determine if the equipment has stopped, and to time the period between equipment stoppages to determine equipment uptime.

 “If you’re going to spend the effort to wire one photo eye, then why not connect a few other items at the same time?” I asked. “The filler must have something to tell it when to start and stop, and probably has a signal to tell it when there isn’t room for it to discharge.  Most likely, there are a few relays in the electrical cabinet that we could get a signal from to tell us the status of the filler and a few of the reasons why the filler can’t run.  If those signals were wired to inputs, we can get more information to feed into your Line Event Data System.  We’d still be looking just at the filler unit operation, but we’d see some of the things that influence it and could have more insight as to what happens throughout a shift.”

 “That’s sounds great, but who can I get to do all this wiring at my new plant?” my co-worker asked.  “The mechanics aren’t into electrical work and I sure don’t have those skills.”

 “Try your plant’s best electrician.  He should be able to find the right wires to connect to and update your drawings.  Watch how the filler runs.  Ask the operators questions.  What device tells the filler to stop filling when the discharge is full?  What does the filler do when there aren’t any jars coming in?  What happens when there isn’t any product to put in jars?  Then explain to the electrician that you want to wire those conditions to inputs in your PLC and have it communicate with your data system.  If you can’t explain it to him, set up a conference call with me and we’ll work through it over the phone.”

 He agreed to try that approach.  “I can work through getting this connected up.  But, how do I get the operators to see the data and edit reasons?  And how do I get reports that I can use to analyze all this data?”

 “That’s a good point,” I said. “The most important thing about collecting data is make sure it is being used to understand and solve problems.  Often people spend a lot of time to collect data, but then don’t do anything with it.  Use your Line Event Data System to keep track.  You’ll have to think through how you want to display and share the information you collect.  But, that gets back to your original question of where to start.  The first thing you want your operators to know how many times their equipment stopped- what was the number of stops?  If you make this the most important measure in the plant culture, you will drive people to behave in the most productive way.  The less the equipment stops, the more consistent the operation, and the less effort is required.  Effort will switch from fire-fighting to preventing stops.”

 My friend agreed, but had a few questions.  “What about production counts and fault causes?  Aren’t we collecting that information, too?  Don’t I need to know causes to prevent the stops from happening?”

 “Sure,” I replied, “the more data you have, the more you can analyze the situation.  If you connect to the right devices, you’ll be well on your way to being able to dig in deeper.  But, start with the most basic and important measure of stops and build from there.  Make sure that information is correct before you go further.  If the information you provide isn’t accurate, you’ll quickly lose traction with the operation and you’ll have a harder time getting people engaged in your plans as you try to implement more tracking systems.  Besides, your operators probably know most of their stop reasons, they just don’t focus on eliminating them- they probably are more interested in getting the equipment back up, not eliminating the cause.  Once you have the organization focused on reducing stops, you can dig in on causes.  Getting accurate stop causes is much harder to determine automatically, so take your time to get it right.  That’s a topic for another day.”

Getting accurate stop counts on each line and each unit operation of a line is the first step to eliminating nagging minor stops.  It’s an easy measure to understand, and is less subject to manipulation than other calculated measures.  There’s an old adage that “you get what you measure” and I’ve seen the power of measuring and discussing stop data on a daily basis in operations I’ve managed.  With proper coaching, operators will engage in getting to the root cause of nuisance stops and eliminating them.  They’ll ask for help on problems that they can’t fix and resources will flow to problem areas.  In the end, their work day will get more predictable and less stressful. 

 The benefits to the bottom line are many as well.  With less stops come consistent flow of product, which means more consistent quality.  With less operator interventions, there is less risk for safety incidents.  Lastly, with longer time between stops, operators have more time to prepare for what’s next, the next change-over, the next maintenance intervention, or just watch the line for more improvement opportunities.  By measuring and reducing stops, every system of the plant benefits.

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