Robotic systems form a strong component of
coinage production at the San Francisco Mint, including the automatic
packaging operations used in assembling sets of coins.
Multiple primary packaging lines can be
dedicated to specific numismatic products. During Coin
World’s May 14 visit, the four-coin 2012-S Presidential $1 Proof
set, containing coins depicting Chester A. Arthur, Grover Cleveland
(two coins, one for each nonconsecutive term) and Benjamin Harrison,
was being packaged.
During Coin World’s visit to the San
Francisco Mint to document coin production as part of the facility’s
75th anniversary, Don Penning, manager of the packaging division, and
packaging industrial supervisor Tonya Jones, served as escorts through
the automated packaging operation and helped explain the various
processes at play.
For the Presidential dollar Proof sets, trays
containing struck Proof coins are moved to the first stage of the
packaging operation. A tray of coins of one design is inserted to
start the process at the first station on the central conveyor system,
and then at subsequent stations different coins are introduced.
Robotic arms with visual sensors detect the individual coins being
introduced into each station along the conveyor system.
For the Robotic Packaging Assembly Process
involving the four-coin Presidential Proof set, a plastic one-piece
insert, with four thermoformed pockets (one for each coin), is
robotically placed onto a pallet (a white polymer plastic template).
The same robot, fitted with a visual sensor, then identifies the
existence of the insert. If an insert is detected, the first robotic
station performs four operations:
(1) The robot will pick up the first coin to
(2) The vision system will verify the coin
depicts the correct president.
(3) The vision system will then instruct the
robot to rotate the coin so that it is properly oriented within the insert.
(4) The robot will then place the coin into
These steps are repeated at the next three
coin stations for the Presidential Proof dollar program.
Once all four coins are present, a bottom,
hard plastic lens is robotically loaded onto the pallet. The insert
holding the coins is then lifted and placed into the bottom plastic
lens. A vision system then scans the four coins for proper alignment
within the insert.
A top plastic lens is then robotically placed
onto the bottom plastic lens containing the insert. The two-piece
plastic lens is then pressed together, the final step in lens
assembly. The lenses are not heat-sealed, but friction fit.
The lensed sets are stacked onto carts and
moved to the final assembly stage.
The carts are secured inside a caged area, in
which two large robotic arms remove the sets one at a time from the
carts and evenly space them along a second conveyor, which moves the
lensed sets to a station that contains stacks of flattened set boxes
bearing the graphics identifying the contents of each set.
Automated machinery opens each individual, flattened box, places
glue on specific flap areas, pushes one set into each box and closes
The boxed sets then move along the conveyor to
where they are mechanically pushed into a cardboard shipping
container, and the flaps of the shipping box are sealed shut.
The shipping box is labeled and moved along to
the final station, where each labeled shipping box is palleted
robotically for delivery to the U.S. Mint’s contracted order
fulfillment center, Pitney-Bowes Government Solutions in Plainfield, Ind.
Pitney-Bowes ships numismatic products to U.S.
Mint customers to fulfill orders.
Mint technicians are stationed throughout the
system, at each step of the packaging process, to ensure the operation
runs as programmed. If problems arise, the employees can correct
problems as quickly as possible to minimize downtime.
Hovering behind the scenes of the processes of
assembling the sets and then placing them into shipping boxes is a
quality assurance team, whose members ensure that the materials used
to produce the coins and package them meet contracted specifications.
Loretta Dickerson, quality assurance manager
with oversight of assay operations; Latonia Johnson, program analyst
specialist; and Michael Goggins, supply quality engineer, represented
the quality assurance team during the May 14 visit.
The facility receives both blanks (unstruck
disks of metal without an upset proto-rim) and planchets (pieces with
an upset proto-rim). When struck by dies, the blanks and planchets
Certain denominations, for example 90 percent
silver, 10 percent copper dimes and quarter dollars, have a slight
upset on them when they are received to prevent damage to the surface
as they are shipped. The blanks (with no upset proto-rim) and the
planchets that arrive at the facility with a slight upset undergo a
full upset before they are struck (the double upsetting is what the
Mint also calls a “complete upset”). The .900 fine silver
commemorative silver dollar blanks, the .999 fine silver bullion
dollar blanks, and copper-plated zinc cent blanks are already fully
upset and ready to strike when received.
All blanks and planchets that are shipped to
the San Francisco Mint are scrutinized by the team for fineness (in
the case of precious metals coins), weight, diameter, thickness and
surface hardness. Blanks and planchets are tested after being selected
from random samples. The Quality Assurance Team examines all shipments
of blanks based on incoming acceptance testing guidelines as outlined
in the San Francisco Mint’s contracts with its various suppliers.
Materials that don’t meet the contracted standards after inspection
The methods used to test composition and
fineness have changed over the years.
Dickerson said the San Francisco Mint formerly
conducted composition and fineness testing by using radiometry by
titration (a method of quantitative chemical analysis), which was
labor intensive and required the silver to be recovered from the
chemical solution used.
Dickerson said the San Francisco Mint
currently uses a Glow Discharge Spectrometer unit to determine the
metal composition of the blanks. The equipment is calibrated to
analyze material over a particular spectral range.
The spectrometer does not require reclamation
of materials as was required when testing was done by titration. The
Glow Discharge Spectrometer unit excites ions and shoots them at a
blank in an atmosphere of inert argon gas. The reaction of the ions
determines the composite elements in the metal on the blank’s surface
and in its successive layers. The sample is not consumed in the
nondestructive process. The new process creates savings both in
reclamation costs and from the planchets lost during the former assay process.
With Glow Discharge Spectrometry, the four-day
process required with radiometry by titration is instead reduced to
just 1.5 days, Dickerson said.
Visual inspections are also conducted on
packaging provided by outside vendors; inspectors look for cracks in
plastic lenses, scuffs or other damage and damaged boxes.
In addition, random, visual inspections are
conducted of coin sets, after preliminary packaging but before the
sets are housed in their cardboard holders. Mint employees compare the
coins in the set to a color graphic of the coins that are supposed to
be in the set, to make sure coins are in the proper location in the
set and aligned correctly.
When considering packaging vendors, Goggins
said he seeks materials that present a good appearance, meet planned
color specifications and are functional. Goggins said potential and
existing vendors are required to submit prototypes when new packaging
options are under consideration.
Extensive reviews are made of product returns
to determine what defects are in the packaging, and what
imperfections, however slight, may be unacceptable.