FINGER 2.0 Thumb Rehabilitation Mechanical Design

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Team Name Thumb Wrestlers
Duration 2020 - 2021
Faculty Adviser
  • Dr. Joel Perry
  • Vishwanath Ketkar, Jacob Brower
Client Dr. Eric Wolbrecht
  • University of Idaho - ME Department
Team Members
  • Avery Frazier (ME)
  • Ryan Burr (ME)
  • Royal Elder (ME)

The goal of the project is to complete and refine the mechanical design of the added 5-bar thumb module system to allow the new FINGER 2.0 rehabilitation robot to be used for both left handed and right handed finger dexterity and movement for post stroke victims.

Problem Definition[edit]

Mitigate the joint slop and looseness to allow the FINGER 2.0 to be as effective as possible in making accurate movement assists to help regain finger dexterity.

Design a new baseplate and left sided thumb module to allow FINGER 2.0 to be used for both left and right hand impaired stroke victim rehabilitation.

Check final form, fit, and function of FINGER 2.0 to ensure comfortability and ease of use for both rehabilitation patients, as well as medical professionals who will be operating the robot.


Over 800,000 people suffer from a stroke in the United States every year alone. Of the survivors, over 2/3 experience long-term impairment of the affected upper-extremity. The use of robotic rehabilitation can automate the repetitive and difficult process of conventional physical therapy that comes after a patient has experienced a stroke. Robotic therapy can also serve as a scientific instrument for quantifying the recovery process and provide insight that is often unavailable with conventional physical therapy.

The original FINGER 1.0 sought to maximize controller fidelity and minimize mechanical impedance. It did so by having only one degree-of-freedom, high controller fidelity, and low friction joints and bearings. It only assisted with middle and pointer finger rehabilitation by utilizing a 8-bar mechanism and having the user make a common grasping motion. FIGNER 1.0 controlled the orientation and position of the middle phalanx of each finger.

FINGER 2.0 was designed before being assigned to our group. It differs from FINGER 1.0 because it also incorporates the thumb in the rehabilitation process. It consists of a spherical 5-bar mechanism that translates a normally 2 dimensional path to 3 dimensional space. The thumb module has 5 links, all attached at both ends to other links. Two actuators allow the system to take input from the user and manipulate that data into a position to help the patient regain their finger dexterity and natural grasping movements. The original mechanism is very well designed, but has some issues that our team has been tasked with redesigning.


For this project, our deliverables will be two prototypes of the FINGER 2.0 robot. Pre-existing geometry and structure were provided at the start of the project. The goal of prototypes one and two are to increase the overall rigidity and precision of the mechanism. Both prototypes will be capable of operation by both right and left-handed users.

Prototype one will focus on the joints between links to simultaneously reduce tolerance and friction. This will be done by combining machined connections with 3D printed links to create precise geometry. Prototype two will focus on the links themselves to reduce the flex of individual members in the system. This will be done by combining different materials, print in-fills, and link geometries to minimize the flex of the links while operated.


Design Considerations[edit]

Project Learning[edit]

Final Design[edit]


Design Validation is a big component of any project. For the FINGER 2.0, our design validation is broken into two main component tests: the base-plate and the link connections. For the base-plate, our design validation is a combination of a solidwork's mock-up, where all mounts and parts will be placed on the base-plate to test if everything needed will fit, and a post production weight test, where we will be leaning on the free end of the plate to determine if the deflection is enough to warrant an addition of more support 80/20 bars.

The validation for the link connections will come from a custom testing jig. The jig is machined out of aluminum and designed to have the same spacing and size of bearings that are on the actual links of the FINGER 2.0. We will then be taking our designs and putting them to the test on the rigid fixture, where we will attached the link and our custom ends to test deflection and how rigid the connection to the joint is.

Team Members[edit]

Avery Frazier

Major: ME
Hometown: Lewiston, ID
Responsibility: Recorder, WikiMaster, baseplate, finger cuffs

Ryan Burr

Major: ME
Hometown: Twin Falls, ID
Responsibility: Team Leader, link redesign, link testing

Royal Elder

Major: ME
Hometown: Auburn, Wa
Responsibility: Client Contact, link redesign, assemblies

Additional Documentation[edit]

Project Schedule


Meeting Minutes



Client Interview