But it gets even worse, from those 45 hours of net operating time of producing
defects and we have to ramp up production, producing scrap potentially during start
up. In this example here.
The total number of losses accumulate to an overall equipment effectiveness of 30%.
This is simply driven by the 55 percent of the times that we have this down time.
82%, namely the ratio between 45 and 55, that we lose before because of lower
speed. And 67%, 30 relative to 45, that are
driven by quality losses. So we notice that we overall equivalent
effectiveness is 30%. We get eighteen minutes of value out of
each hour of work that we spend at the machine.
Often times, what you will notice is that even with an OE yield of 30 percent the
people actually operating the equipment might require that you invest in more
equipment. After all, the equipment and the workers
are on it seem to be busy most of the time.
But, as Ono quoted, moving is not working. The OEE helps us to realize that in this
case, we have almost a 3x productivity improvement potential without investing
anything further in additional equipment. There's a surprising when I worked with
the case of an aircraft. We can think of the equipment as an
aircraft seat. The seat is only adding value if it is in
the air and it has a paying customer sitting in it.
What percentage of the time do you think the typical airline seat actually adds
value? When I ran the analysis for the big US
carriers I found the following. On the left here I started with 365 days
in the year and the 24 hours that are in a day.
Most of the time is lost. Because the plane is either at the gate or
it's in maintenance. This is not too surprising.
Most of this in fact is driven by the fact that nobody wants to fly from Philadelphia
to Chicago at two in the morning and it's just not profitable for the airlines to
fly at crazy hours. The other chunk here is maintenance that
is required for the planes. This leaves us with the amount of time
that is typically referred to as a block time.
This is a time that the plane is actually moving.
But moving includes taxiing and landing, not, at least from the customer's
perspective, necessarily valued at. After subtracting this as a ten percent of
the time to compute that an aircraft is in taxi and landing, you get the time that
the seat is in the air. But not every minute that the seat is in
the air is an invalue because seats often fly empty.
Typical aircraft utilizations are in the low 80 percentages.
And so we have to subtract another 10-20 percent to adjust for the fact that we are
flying empty seats. If you combine all of these effects
together and you compute the AE or EE of the aircraft seat, you typically get a
number that is around 30%. You might think that, that number is low,
but I can assure you it's dramatically higher than where it was some ten years
ago. The OEE framework applies to equipment at
wel-, as well as it does to people. So folks at MacKenzie, which is where I've
picked up the OEE framework, in that case, because the OPE, the overall people
effectiveness. Let me illustrate this with an example.
In a research collaboration that I'm currently conducting with the VA Hospital
system, I'm trying to measure how doctors are spending their time.
I'm trying to determine their OPE. Let's start with the total time that we
have the doctor on payroll. Well, doctors are sometimes on vacation
and sometimes sick themselves, which gives us the total time the doctors are in
practice. Now, not every minute of the time is
booked for appointments. Even though doctors in primary care in
particular tend to be very busy, they still have some empty appointment slots.
That leads to idle time for the doctors. This gets us to the total time that the
doctor has booked for appointments. Some of the patients, however, have an
appointment and then don't show up. No-shows or cancellations, thus, further
reduce the OPE of the doctor. After adjusting for cancellation, we get
the total time that the doctor spends with the patient.
This is when things get dicey from a data perspective, more senseless things that I
don't, I know, have relatively little data about what actually happens during the
doctor patient encounter. In the case of the VA system, we use video
cameras to document minute by minute, what goes on when the doctor speaks to the
patient. It's interesting to see that a good number
of the patients that are spending time with a doctor, really don't have to be
seen by a medical doctor, and could be seen easily by a nurse or anther physician
extendor. Moreover, if you go minute by minute,
through the processing time, typically that's a twenty minute encounter, you'll
find that the doctor spends many things doing that are not really requiring the
knowledge of a medical doctor. Rewriting scripts for refills for
medications, patient counseling and social work.
This gets you the real true value of time for the doctor.