Wrist Assembly

Wrist Circuit

The wrist assembly is composed of 19 components (not including fasteners and dowels). 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.

Wrist Attachment

Purpose of Component - The wrist attachment is the part of the wrist assembly that attaches to the wrist of the user. As the user's wrist rotates, so does the wrist attachment. The wrist attachment is mounted between two components (front holder and back holder). Although, it was never modeled (mostly because it wasn't decided on until most of the components had already been built or bought), the mechanism for gripping a user's wrist in the wrist attachment can be described as follows: Threads for three bolts were tapped radially through the outer edge of the wrist attachment. The bolts were attached to a bent piece of sheet metal with padding on it. When the user's wrist is between the padding, the bolts are tightened and the wrist attachment rotates with the user's wrist.
Number of Components - 1
Material - PVC
Purchasing Information - The wrist attachment is actually a PVC Bushing. It was obtained from Home Depot for $4.10. When the PVC Bushing was purchased, it had an extra lip (illustrated in the picture below) at the end that prevented most ordinary sized hands from fitting through the opening. A lathe was used to remove the lip.


Approximate dimensions for this component are shown below.
(click for a larger image)

Front of Wrist Attachment Holder

Purpose of Component - The front and back of the wrist attachment holder are used to constrain the wrist attachment and to attach the wrist attachment to rest of the robotic interface. The large circles were created using a computer numerically controlled (CNC) milling machine, and the front and back of the wrist attachment holder are bolted together with the slider holder attachment in the final assembly.
Number of Components - 1
Material - Poplar Wood
Purchasing Information - The Poplar wood board used for the front of the wrist attachment holder 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)

Back of Wrist Attachment Holder

Purpose of Component - The front and back of the wrist attachment holder are used to constrain the wrist attachment and to attach the wrist attachment to rest of the robotic interface. The large circles were created using a computer numerically controlled (CNC) milling machine, and the front and back of the wrist attachment holder are bolted together with the slider holder attachment in the final assembly.
Number of Components - 1
Material - Plexiglas
Purchasing Information - None. The Plexiglas was obtained from the mechanical engineering machine shop.

Approximate dimensions for this component are shown below.
(click for a larger image)

Slider Holder Attachments

Purpose of Component - The slider holder attachments are used to attach the slider holders to the wrist attachment. The slider holder attachments are bolted to the front and back wrist attachment holders.
Number of Components - 2
Material - Wood (possibly Pine or Maple)
Purchasing Information - The wood stud used for the slider holder attachments was obtained from Home Depot. A 2" X 3" X 8' stud costs $1.83 (other components were made from the same stud).

Approximate dimensions for this component are shown below.
(click for a larger image)

Slider Holders

Purpose of Component - The slider holders are used to attach the sliders to the wrist attachment. The slider holders are attached to steel dowels that go through the sides of the slider holder attachments.
Number of Components - 8
Material - Wood (possibly Pine or Maple)
Purchasing Information - The wood stud used for the slider holders was obtained from Home Depot. A 2" X 3" X 8' stud costs $1.83 (other components were made from the same stud).

Approximate dimensions for this component are shown below.
(click for a larger image)

Sliders

Purpose of Component - The slider is used to allow the entire wrist assembly to move up and down within the robotic interface. Essentially the slider was acting like a crude journal bearing.
Number of Components - 4
Material - Metal (probably steel)
Purchasing Information - The slider was actually a piece of piping used for plumbing (there should be threads on the drawing and in the image, but it hardly seemed worth it). They were obtained from Home Depot for $0.53 each.

Approximate dimensions for this component are shown below.
(click for a larger image)

QRB1114 Photoreflectance Sensors

Purpose of Component - The photoreflectance sensors are used to detect where the wrist assembly is relative to the rest of the robotic interface. 1/8" diameter rods were used to mount the sensors at the top and the bottom of one of the slider holder attachments to minimize the distances they would have to detect.
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 QRB1114 photoreflectance sensor are also available online through QT Optoelectronics.
(click for a larger image)