The encoder assembly is composed of 15 components (not including fasteners). Each of these components is illustrated in the exploded view below. Clicking on the component in the image links to a description of the component. Note: The drawings are intended to provide a rough idea of the specs used to create this part of the robotic interface.
Purpose of Component - The main encoder shaft provides support
for the pulley, the encoder
disc mounts, and the encoder
discs.
Number of Components - 1
Material - Aluminum
Purchasing Information - The aluminum rod was obtained from
Home Depot. A
3-foot, 1/4" diameter rod costs approximately $3.00 at Home
Depot.
Approximate dimensions for this component are shown below.
(click for a larger image)
Purpose of Component - The pulley follows the motion of the
user's wrist and transfers this motion to the two encoder
discs. A rubber band is attached between the pulley and the
component attached to the
user's wrist. The pulley is attached to the main encoder rod with
super glue.
Number of Components - 1
Material - Plastic
Purchasing Information - The pulley is actually a roller for a
patio door. It was obtained from Home
Depot for $1.92 (the super glue was obtained at Jewel Osco for
$1.08).
Approximate dimensions for this component are shown below.
(click for a larger image)
Purpose of Component - The bearings support the main encoder
shaft and allow it to rotate effortlessly. The bearing are press fit
into the bearing mounts. Although the
intent had been to place the encoder disc
mounts flush against each bearing and use a set screw on the main
encoder shaft to hold them in place, misalignments between the
encoder discs and the IR
slotted photointerrupters prevented this. To fix the main encoder
shaft relative to the bearings, one end of the shaft was super glued
to a bearing.
Number of Components - 2
Material - Metal (probably bronze)
Purchasing Information - The bearings are actually rollers for
a patio door. They were obtained from Home
Depot for $4.09 for both.
Approximate dimensions for this component are shown below.
(click for a larger image)
Purpose of Component - The encoder disc mounts are fixed to
the main encoder shaft with set screws, and (altho not originally
intended) super glued to the encoder
discs. The intent was to use the encoder
disc mount rods to align the encoder
discs. The alignment was incorrect, however, and it was necessary
to "improvise" a solution (i.e. use super glue).
Number of Components - 2
Material - Aluminum
Purchasing Information - None. The 1/2" diameter rod was
obtained from the mechanical engineering machine shop.
Approximate dimensions for this component are shown below.
(click for a larger image)
Purpose of Component - The encoder disc mount rods were
intended to align the encoder discs, but they were not used. Instead
the encoder discs were mounted to the encoder disc mounts with super
glue and then the encoder disc mounts were aligned to the main
encoder shaft.
Number of Components - 2
Material - Steel
Purchasing Information - None. The 1/8" diameter rod was
obtained from the mechanical engineering machine shop.
Approximate dimensions for this component are shown below.
(click for a larger image)
Purpose of Component - The IR slotted photointerrupters are
used to detect when the "teeth" on the encoder
discs are breaking the IR beams. The sensors are attached to the
encoder sensor mount with screws.
Number of Components - 2
Material - Plastic (plus emitter and detector)
Purchasing Information - None. The sensors were obtained from
the Mechatronics
Lab.
Approximate dimensions for this component are shown below. The
technical
specifications for the QVB11334 IR slotted photointerrupter
sensor are also available online through QT
Optoelectronics.
(click for a larger image)
Purpose of Component - The encoder discs are used to break
the IR beams on the photointerrupter sensors. There are two discs
mounted on the main encoder shaft. The holes that were intended to be
used to align the discs are 6 degrees out of alignment on one of the
discs. This allows the teeth to pass through the photointerrrupter
sensors 90 degrees out of phase, since each tooth is 12 degrees wide.
Because the holes to align the discs weren't used, the encoder
circuitry had to be built to test the alignment of the discs before
fastening them to the main encoder shaft.
Number of Components - 2
Material - Aluminum
Purchasing Information - None. The 1/16" thick aluminum sheet
metal was obtained from the mechanical engineering machine shop.
Approximate dimensions for this component are shown below.
(click for a larger image)
Purpose of Component - The encoder sensor mount is used to
restrain the photointerrupter sensors and the bearing
mounts. The bearing mounts are attached to the sensor mount with
wood glue and screws, and the photointerrrupter sensors are attached
with screws. The sensor mount itself is then attached to the
wrist assembly with screws (a
little glue was also necessary, because the wood began to fracture
when the screws were affixed).
Number of Components - 1
Material - Poplar Wood
Purchasing Information - The Poplar wood board used for the
encoder sensor mount was obtained from Home
Depot. A 1" X 6" X 2' Poplar wood board costs $3.84 (other
components were made from the same board).
Approximate dimensions for this component are shown below.
(click for a larger image)
Purpose of Component - The bearing mounts are used to
restrain the outer rim of the bearing on the main encoder shaft from
rotating relative to the inner rim of the bearing. The bearing mounts
are attached to the sensor mount with wood glue and screws.
Number of Components - 2
Material - Poplar Wood
Purchasing Information - The Poplar wood board used for the
bearing mounts was obtained from Home
Depot. A 1" X 6" X 2' Poplar wood board costs $3.84 (other
components were made from the same board).
Approximate dimensions for this component are shown below.
(click for a larger image)
