Beginners Guide to TikTok for Search - Rachel Pearson - We are Tilt __ Bright...
(417898087) larson.james stat495 Project
1. DECEMBER
12,
2014
DISHWASHER
TEMPERATURE
CONTROL
2013
DATA
JAMES
LARSON
SUBMITTED
TO
DR.
W.
ROBERT
STEPHENSON
2. DISHWASHER
TEMPERATURE
CONTROL
SUMMARY
12/12/2014
JAMES
LARSON
1
Executive
Summary
Subject:
Variation
in
Dishwasher
Rinse
Cycle
Temperatures
The
process
being
analyzed
is
the
temperature
(°F)
for
the
four
rinse
cycles
in
the
main
commercial-‐grade
dishwasher
being
used
at
an
Iowa
State
Dining
facility.
These
are
classified
as
Prewash
120,
Wash
150,
Rinse
160,
and
Final
Rinse
180.
The
manufacturer
specifications
are
then
assumed
to
be
120°F,
150°F,
160°F,
and
180°F
respectively.
Using
the
raw
data
procured
for
this
study,
there
are
three
readings
per
day
for
each
meal
time
(Breakfast,
6:30-‐10:30;
Lunch,
10:30-‐2:30;
Dinner,
4:00-‐8:00
PM)
and
five
operators
recording
said
temperatures
for
the
main
dishwasher
at
different
times
over
the
course
of
335
days
(January
14-‐December
15).
The
readings
do
not
account
for
the
times
at
which
they
were
taken.
Looking
at
all
the
rinse
cycles
using
subgroups
of
one
week
(3*7=21,
seven
days
times
the
three
meals
and
readings
taken),
there
are
several
subgroups
that
fall
outside
the
specification
limits.
The
respective
control
charts
(X-‐bar
and
R-‐bar)
are
included
as
Figures
1-‐4
in
the
appendix.
Some
samples
were
discarded
from
the
analysis
due
to
lack
of
entries
ruling
out
special
causes
(i.e.
federal
holidays,
university
breaks,
cleaning
week).
This
will
be
discussed
later.
Looking
at
the
X-‐bar
chart
for
Pre
Wash
120,
samples
1
(Jan
14-‐20),
3
(Jan
28-‐30),
5
(Feb
11-‐
17),
8
(Apr
8-‐14),
13
(April
8-‐14),
15
(Apr
22-‐28),
24
(Jun
24-‐30),
30
(Aug
5-‐11),
35
(Sept
9-‐15),
39
(Oct
7-‐13),
and
41
(Oct
21-‐27)
fall
outside
of
the
control
limits
in
the
X-‐Bar
chart
for
the
Prewash
120
cycle.
Samples
1,
4,
25
(Jul
1-‐7),
33
(Aug
26-‐Sept
1),
34
(Sept
2-‐8),
35
(Sept
9-‐15),
38
(Sept
30-‐Oct
6),
and
41
(October
21-‐27)
fall
outside
of
the
control
limits
on
the
R-‐Bar
chart
(average
of
ranges
per
subgroup).
Other
rinse
cycles
are
depicted
on
the
appendix
in
Figures
1-‐4.
From
the
process
and
data
given,
it
can
be
said
the
dishwasher
is
not
operating
within
statistical
control
for
all
rinse
cycles.
Further
investigation
in
these
subgroups
may
explain
the
special
cause
in
the
measurement
(machine
breakdown,
higher
than
average
capacity,
lack
of
filter
cleaning,
etc.).
This
study
provides
several
enumerative
methods,
though
can
be
used
for
analytic
purposes
for
possible
future
decisions
with
respect
to
the
methods
and
maintenance
of
the
dishwasher.
3. DISHWASHER
TEMPERATURE
CONTROL
SUMMARY
12/12/2014
*The
overall
process
diagram
is
included
in
the
Appendix
under
Figure
11
JAMES
LARSON
2
Variability of Dishwasher Temperatures
People
The
people
involved
in
the
process
are
the
several
dining
facility
staff
and
student
staff,
including
but
not
limited
to
student
workers,
student
supervisors,
and
student
assistant
managers.
Non-‐student
staff
includes
the
managers,
chefs,
and
non-‐student
supervisors
within
the
facility.
Process*
The
washing
of
dishes
begins
with
the
source
of
the
used
dishes
and
what
type
was
used.
Certain
dishes
(bulk
plates/bowls,
metal
serving/prep
pans
and
pan
covers,
silverware,
plastic
trays/containers/lids,
plastic/ceramic
cups)
are
sent
through
the
main
dishwasher
after
being
pre
washed
on
either
the
belt
line
or
the
“Pots
and
Pans”
section
of
the
dish
room.
When
used
dishes
are
sent
via
the
conveyor
belt
(belt
line),
the
dishes
are
first
dumped
of
excess
food
matter
in
compost
bins;
afterwards,
they
are
sent
via
the
belt
to
a
series
of
spray
nozzles
where
they
are
then
further
cleaned
by
either
student
workers
or
supervisors
(depending
on
staffing
that
day)
and
sent
via
another
conveyor
belt
to
the
dishwasher.
These
dishes
are
then
placed
in
their
respective
containers
(bulk
dish
carts)
or
place
of
origin
(Back
of
House,
other
venues)
Metal
serving/prep
pans
and
plastic
trays/containers
are
taken
to
Pots
and
Pans
where
they
are
first
rid
of
excess
food
matter
and
sprayed
by
a
separate
nozzle
apparatus;
the
pan
is
then
set
to
soak
in
a
large
sink
of
warm,
soapy
water
to
loosen
the
remaining/burned
matter
and
is
cleaned
further
before
being
sent
to
the
main
dishwasher.
When
these
are
put
through
the
dishwasher
cycles,
they
are
shelved
close-‐by
before
being
placed
in
their
place
of
origin
(Back
of
House
or
other
venue)
Silverware
is
deposited
through
chutes
above
the
main
conveyor
belt
entering
the
dish
room.
The
silverware
is
soaked
in
a
cleaning
agent
before
being
sent
through
the
dishwasher
for
an
initial
cleaning.
The
silverware
is
then
organized
into
round
containers
for
each
type
of
silverware
(forks,
knives,
spoons)
and
sent
through
the
dishwasher
again.
Cooking
utensils
(knives,
spatulas,
etc.),
metal
sheet
trays
used
(often
from
another
dining
facility),
and
other
metal
dishes
are
sent
through
a
different
dishwasher
denoted
as
“Pots
and
Pans”.
Maintenance
The
maintenance
of
the
dishwasher
typically
occurs
once
per
shift
by
one
or
several
student
workers
or
a
supervisor,
though
this
varies
depending
on
new
student
staffing
inflows
and
student/visitor
traffic
and
facility
capacity
at
a
given
time.
Each
rinse
cycle
has
a
filter;
the
water
for
each
is
first
drained
one
at
a
time
before
each
filter
has
its
contents
dumped
and
sprayed
out
to
remove
other
excess
food
matter.
Measurement
Dishwasher
rinse
cycle
temperatures
are
read
from
gauges
on
the
side
of
the
in
degrees
Fahrenheit
(ºF).
A
measurement
is
logged
during
one
mealtime
per
day
with
three
meals
per
day
(hence
three
readings
a
day).
Five
operators
took
three
readings
per
day
(21
readings
a
week,
the
subgroup
used)
at
several
different
times
(i.e.
370
of
the
1005
readings
are
from
Operator
1,
while
8
are
from
Operator
5).
These
operators
are
typically
the
non-‐student
supervisors
during
the
respective
meal
times.
4. DISHWASHER
TEMPERATURE
CONTROL
SUMMARY
12/12/2014
JAMES
LARSON
3
Further Quantitative Results
Data Log Issues
As
discussed
earlier
in
this
document,
there
are
several
instances
of
no
entry
during
the
mealtime
specified
from
the
raw
data.
347
temperature
logs
were
not
entered
during
a
given
operator’s
shift.
This
lack
of
data
may
have
led
to
the
exclusion
of
subgroups
in
the
control
charts
in
Figures
1-‐4
in
the
appendix.
A
Pareto
chart
has
been
constructed
below
depicting
several
of
the
issues
found
within
the
data
logs,
though
the
lack
of
entries
is
most
alarming—roughly
98%
of
the
problems
with
the
data
have
stemmed
from
the
lack
of
entries.
Special
causes
(federal
holidays,
University
breaks,
cleaning
week)
were
diagnosed
and
accordingly
left
out.
5. DISHWASHER
TEMPERATURE
CONTROL
SUMMARY
12/12/2014
JAMES
LARSON
4
Rinse Cycle Pre Wash 120 Wash 150 Rinse 160 Final Rinse 180
0.1744 0.1245 0.2618
0.2849 0.4004 0.0889
Operator and Dishwasher Variability (%)
A Gauge R&R study was used to differentiate whether the variability in dishwasher cycle temperatures
was from the dishwasher itself (repeatability), the operator at the time (reproducibility). The study is
attached at the end of this document. The dishwasher often caused most of the variability in
dishwasher rinse cycle temperatures from the data and methods used; at times 90-97% of the
temperature variability was attributed to the dishwasher. These are shown in Figures 5-8 in the
appendix, though these variance measures use a restricted maximum likelihood (REML) rather than a
traditional variance (range-based) due to the inconsistent amount of entries per operator.
Potential and Capability of Process
The two metrics presented, Cp-hat and Cpk-hat, represent respectively the potential and capability of
a process based on the variability of readings the process has given by readings over time. Specification
limits used were 5ºF about a target temperature (manufacturer specification) for each rinse cycle for
both the Cp-hat and Cpk-hat calculations with respect to an upper specification limit (USL) and lower
specification limit (LSL); for example, 115ºF-125ºF for Pre Wash 120, 145ºF-155ºF for Wash 150, etc.
The respective formulas used for the calculations are shown in Figure 9a in the Appendix.
Using the range-based sigma, the Cp-hat and Cpk-hat values are as follows:
Considering the value for Cp-hat (process potential) is a measure (%) of how well a process might be
able to perform a process with respect to the variability of the process data, a Cp-hat value greater
than 1 would indicate the process may be able to perform the process given; likewise, a Cpk-hat
greater than 1 indicates the equipment is not capable of performing the process with respect to
process variability.
In summation, the respective Cp-hat and Cpk-hat values calculated in the table above show that each
rinse cycle is experiencing too much variability within the process-given mean; alternatively, the
specification limits used would have to be several times larger to account for the variability in each
rinse cycle. This may imply higher maintenance costs and higher probability of machine breakdowns
for the dishwasher over the timeline of the data and the time following the historical data.
6. DISHWASHER
TEMPERATURE
CONTROL
SUMMARY
12/12/2014
JAMES
LARSON
5
Possible Solutions
Future Entry and Special Cause Identification
As stated earlier, most of the issues are not due to the operator; however, if more supervisors present
in the dish room this will help alleviate the instance of no entry in the temperature control logs. Since
the enumerative study was using subgroups of the overall week average temperatures (n=21),
construction of a new entry method with more supervisors should be considered. Using the calculation
of gauge R&R reproducibility error as a reference and the lack of operators per day logging the
temperature (typically 1-2 operators during the day currently), the error between readings between
the current handful of operators (and in turn the repeatability [machine] error) should be decrease and
may make it easier to identify special causes. Consider the current entry method:
TIME DATE DISH MACHINE POTS AND PANS INITIALS
PREWASH
120
WASH
150
RINSE
160
FINAL
RINSE
180
WASH
150
FINAL
RINSE
180
BREAKFAST
LUNCH
DINNER
The current method for recording temperatures accounts for one entry per mealtime and leaves the
time of entry (8:34 AM, 12:34 PM, etc.) ambiguous, making it difficult to identify special causes (above
normal capacity, continuous/maintenance hours, time since last cleaned, etc.) in temperature
readings, and only leaves room for one operator to enter the rinse cycle temperature data.
Given there are two dish room supervisors at a given time during each shift and one non-student
supervisor present in the dish room, let’s say each gives one reading per meal time giving three
readings per meal time. Accounting for three meals a day, there will be nine readings per day. Over
the course of a typical month’s timespan (seven days per week with roughly four weeks per month),
there will be roughly 252 readings/month. If it is also desired to identify and maintain the process
such that the dishwasher’s temperature data falls outside of statistical control (i.e. once a month),
this gives an average run length (ARL) of the amount of readings before the process has a subgroup
outside of statistical control that can possibly be attributed to a special cause. If the overall process
distribution is normal or normalized, this would imply a desired failure rate or the probability of a
subgroup of measurements falling outside of statistical control to be roughly 0.39%
7. DISHWASHER
TEMPERATURE
CONTROL
SUMMARY
12/12/2014
JAMES
LARSON
6
If it is desired to see how many readings per subgroup it would require for at least one reading was seen
one process standard deviation above the average reading for a given rinse cycle, a probability model
using a random sampling distribution to calculate the amount of readings in the subgroup results in a
subgroup size of 8.9766 or 9 readings. Knowing the ideal daily amount of readings (9) by the three
operators per meal (breakfast, lunch, dinner) if the points outside of statistical control are found to be
special causes and if the process is brought to be within statistical control. This will also alleviate the
issue of data aggregation from this study for future studies. The respective ARL and subgroup
calculations used are found in Figure 9b of the appendix in this document.
These daily readings can be much more responsive to special causes than to that of the weekly
subgroups; this way, the special causes of unusually high or low dishwasher rinse cycle temperatures
can be much more easily identified. A template for the suggested new logging is included in Figure 10
of the appendix.
Methods and Maintenance
Some if not most of the machine wear and unusual temperatures logged over time may be attributed to
the lack of filter cleaning during a given shift (new inexperienced staff, large inflow of customers at a
given time). Though the filters for each respective rinse cycle are emptied and cleaned roughly three
times a day, this is highly variable considering lack of staff and high customer capacity at given times
in the dish room and facility respectively.
Some plastic dishes are not dumped or rinsed before being placed through the dishwasher; likewise,
though the silverware is placed in a soaking agent to loosen excess food matter, it is not rinsed and
said matter will be caught in the filter and over time if not cleaned regularly may cause more wear
on the machinery.
A suggested maintenance goal would be to try cleaning the filters twice per mealtime to ensure less
wear on the main dishwasher. Other pre washing methods, including using the spray nozzle by the Pots
and Pans section on the silverware, may lead to more stable temperatures as less food matter is
present when put in the dishwasher. Maintenance methods used during Cleaning Week before opening
up for weekend (Saturday, Sunday) may also assist in bringing temperatures within statistical control if
possible; otherwise machine temperatures should be monitored and recorded during preparation
times before the brunch and dinner shifts to ensure an even amount of data within each subgroup
each day to achieve these goals.
Machine
Using the methods suggested above may be able to decrease the variability in temperature data in
future studies. For example, a survey similar to the one presented for future dates (possibly a frame
of next year, 2015, or this coming semester) should be studied to evaluate the effectiveness of the
suggested methods based on the results of future data (i.e. control charts and Cp-hat/Cpk-hat
indices). If there is an improvement (i.e. more points within statistical increased process potential
and/or capability), continue doing so and improving on other results. If results do not improve after
changes to the methods along with continued frequency of extensive machine wear (breakdowns),
maintenance, and process then this historical data may give empirical evidence for the possible future
petitioning for funding for a new commercial dishwasher to ISU Dining’s upper managers or board of
directors.
17. DISHWASHER
TEMPERATURE
CONTROL
SUMMARY
12/12/2014
JAMES
LARSON
16
FIGURE 10
MEAL TIME CAPACITY DISHWASHER Pots and Pans Signature
(%) 120 150 160 180 150 180
B
B
B
L
L
L
D
D
D
