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Visual controls



Published January 18, 2011
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Visual controls are some of the most commonly used tools in the Lean toolbox. They, along with other tools such as 5S, quick changeover, point of use storage and a Kanban system, can have tremendous impact on any operation and help to identify waste (muda), imbalance (mura), or unreasonableness (muri) so that they can be eliminated from the workplace.

Visual controls play a critical role in providing information to team members at every level in the organization so that good decisions can be made that have a positive impact on these efforts to root out and eliminate waste, imbalance and unreasonableness.

Like the other Lean tools, these visual controls are there because something isn't quite right, something's not perfect, and a countermeasure is needed to correct the undesirable condition.
I've been noticing lately, though, that many people and even some companies have what I feel is an overreliance on this simple tool. They are applying visual indicators to equipment and in other areas which highlight only that an imperfect (even unsafe) condition exists, but they don't take steps to implement any real countermeasure to correct it.

Low bridge
Here's an example of one from a photograph that I saw recently of an overhead sign warning oncoming drivers of a low bridge. The sign warns drivers that if their vehicle struck this sign then they would also strike the railroad overpass just up the road.

Even if the driver is distracted and doesn't see this enormous sign that spans the entire width of the road, or if the driver does not or cannot read English, this particular sign does provide more warning than most signs. Not only is there the visual component – the high visibility yellow sign with large block letters – but also there are two other sensory warnings that the driver will have if and when his or her vehicle impacts the sign. If you hit the sign you would surely hear the sound of the impact (unless your radio is set to an ear shattering volume) and you should also feel the impact through vibration and shaking in the steering wheel.

It's a good sign, yes, and its better than most, but it doesn't stop every vehicle from hitting the overpass. A vehicle could conceivably strike the sign and then continue on to strike the bridge. One would hope not, but it could happen.

This is where overreliance on visual controls can lull you into a false sense of security and the misguided belief that you have solved the problem, because you haven't; you've merely provided a warning about the problem.

Poka-yoke

Like all other Lean tools the use of visual controls must serve a purpose. We need to know what it is we're trying to solve when we're implementing a countermeasure so that we can develop both the simplest and most effective solution.

Shigeo Shingo, in his book A Study of the Toyota Production System (Productivity Press, 1989), discusses the use of poka-yoke devices (error-prevention devices) as a way to prevent the occurrence of defects. Shingo writes that there are "different functions and types of poka-yoke devices":

Correcting function - warning or control
Setting function - contact, constant number, motion step

In the case of the road sign we have to ask ourselves what we're trying to do. In our case we're looking for a correction function or correcting solution to prevent the error of an accident from occurring, so our error prevention choices are either warning or control. Is it to prevent ALL vehicles from striking the overpass or are we looking to prevent almost all of them from striking the bridge?

If the goal is to prevent most, but not all, of the accidents from happening, then a warning sign should be more than sufficient. Putting up the sign, though, isn't the end of our corrective action. We need to make sure we do the Check part of our PDCA cycle (Plan-Do-Check-Act) and go see that our countermeasure is effective (versus just "checking" to make sure that the sign was properly created and installed).

If the goal is to prevent all accidents at the intersection of the road and the overpass then a sign will never be effective no matter how big and glaringly obvious it may be. If the goal is to prevent all accidents and just one happens, then our visual countermeasure has failed. We want 100 percent accident prevention but we don't go far enough with our countermeasures to meet that goal.

If we want to prevent all accidents, then perhaps we could put in some type of vehicle arrestor system, similar to the accident barriers that are used on aircraft carriers, to snare an offending vehicle and bring it to a stop. We could install a tire-shredding spike strip, but we've all seen video of police chases where spike strips were deployed and the vehicle is able to continue moving forward on the rims, showering sparks everywhere, or we could install solid posts that spring up from the ground when an oversized vehicle trips a sensor, stopping the vehicle almost instantaneously.

While these suggested solutions might prevent a vehicle from striking the overpass, they don't prevent an accident, except for one involving the railroad bridge.

Some might feel that these solutions are over-engineered, that a sign is good enough and a simple solution to the problem, and that a simple solution is the best solution. While it's true that some things are certainly over-engineered and that simplicity is best, the simplest solution isn't always the best solution unless it meets the goal you're trying to reach or solve the problem that you're trying to solve. If it doesn't then it's not a solution, regardless of its simplicity, especially when personal injury is at stake, as it may be in our railroad overpass example.

Danger, danger
How does this relate to your operations? Well, like everything else in Lean the answers do not come from a book or from this column, for that matter. The answers will come from the floor, from the "gemba" or the "real place" where the condition occurs. You need to go to the real place and experience these conditions for yourself. What do you see? You probably have several pieces of equipment with a picture similar to this:

What's the purpose behind this sign? Is it to prevent anyone from getting their hands caught in the machinery? If so, this sign is not an effective countermeasure because it will not prevent that from happening all of the time. What about the sentence that tells the operator to "NOT operate with the cover removed?" Will this sign really prevent an operator from operating without the cover? No, it won't, but this is another example where a visual control can lull one into a false sense of security, in this case the desire to prevent a serious injury.

So what to do? As stated previously, we need to know what it is we're trying to solve when we're implementing a countermeasure so that we can develop both the simplest and most effective solution. If we're trying to prevent someone from becoming injured by putting their hand into a piece of machinery then we have to identify all possible solutions and evaluate them not only on their own merit but on whether or not they can meet our stated goal.

Risk versus reward
We also have to consider the risks associated with each potential solution (think of it in the context of Joseph Juran's producer's and consumer's risks). If the goal is to prevent most but not all pinch related injuries, then what's the operator's risk (the consumer's risk) with that goal? Can we honestly say that a sign that costs a few dollars is an acceptable trade-off to even one injury? Would you be willing to stand up in front of all of your employees and declare that you've weighed all of the risks and have decided that you've accepted the fact that the sign won't prevent all injuries from occurring but that you're willing to take that chance? After all, it's not your fingers that will get caught. You wouldn't make that statement but that is the message that gets sent by this sign.

If the goal is to prevent all potential injuries and to avoid all "consumer's risk" then the sign won't work. In our railroad bridge example, how could we prevent all vehicles from striking the overpass? One way would be to rip up the road and shut down all access, but that may be too extreme. The road may be the only one for miles, it may be a main avenue for commercial or retail traffic, or it may be a shortest route for emergency vehicles to and from a hospital. So perhaps our goal is to guarantee access to all vehicles while avoiding all collisions. This may mean burying the rail line below road level or raising the road level over the rail line. Vehicles won't hit a restricted height rail bridge that's no longer there. Both of these solutions may seem extreme and over-engineered, but not if the goal is 100 percent accident (and subsequent injury/fatality) avoidance.

What about our pinch point example? What could we do to prevent all potential injuries at this pinch point? One way is to install safety interlocks that shut off the machine if the cover is removed. New equipment comes with these interlocks installed (along with the requisite warning label) but often these interlocks are disabled by operators, and management ignores these glaring safety violations. If the operators feel that they cannot operate their equipment without disabling safety interlocks then it is our obligation as leaders to work with them to correct this condition.

What other conditions exist both in your facility and outside on the property that you've allowed to exist with just visual control? Do you have the usual "Do this, don't do that" signage plastered throughout your building? If so, why were these signs installed? What condition exists that you feel the need to warn people about? What can you do to provide an effective countermeasure that will eliminate these conditions and, therefore, the need to have the signs?

Visual controls are an effective tool to assist in identifying undesirable conditions so that effective countermeasures can be put in place. These undesirable conditions could be one or more of the eight wastes or muda (defects, overproduction, waiting, non-utilized people, transportation, inventory, motion or extra processing), an imbalance in the workload on people or equipment (mura) or an overburdening of people or equipment that leads to unnecessary stress or strain. Identifying these conditions is just the beginning to truly controlling them, and we can do the latter by implementing countermeasures that are reasonable, effective and that provide the desired outcome. Companies that use visual controls in this manner will see positive impacts in their safety, quality, delivery and cost metrics.

Tom Southworth is a Lean consultant with CONNSTEP, Connecticut's Manufacturing Extension Partnership. He is a Senior Member of ASQ, an ASQ Certified Manager of Quality & Organizational Excellence, a senior member of the Society of Manufacturing Engineers, SME Lean Bronze Certified, and a certified TWI Job Instruction and Job Relations Trainer. He can be reached by email at tsouthworth@ connstep.org.


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