Automated Biomechanics Testbed for Soft Tissue Characterization

This project created an actuated indenter device for characterizing human soft tissue properties around the forearm. The system enables precise measurement of viscoelastic tissue properties at multiple anatomical locations to inform human-centered design of wearable interfaces.

Indenter assembly with the linear indentation carriage mounted on the rotating ring structure, which can be moved at the base. The human limb is placed through the rotating ring and grounded during characterization measurements.

Indenter assembly with the linear indentation carriage mounted on the rotating ring structure, which can be moved at the base. The human limb is placed through the rotating ring and grounded during characterization measurements.

The linear indentation carriage module includes: (A) linear carriage driven by a stepper motor, (B) single-axis load cell, and (C) indenter head that interfaces with soft tissue. The rotating ring structure includes (D) outer ring, (E) grounded cente

The linear indentation carriage module includes: (A) linear carriage driven by a stepper motor, (B) single-axis load cell, and (C) indenter head that interfaces with soft tissue. The rotating ring structure includes (D) outer ring, (E) grounded center ring, and (F) inner ring.

The experimental setup shows the indentation location fixed at a point along the length of the arm, as well as anchoring cuffs at the wrist and elbow.

The experimental setup shows the indentation location fixed at a point along the length of the arm, as well as anchoring cuffs at the wrist and elbow.

The 12 angular locations measured in this paper (repeated across 3 rows) are shown in the forearm cross section of the right arm.

The 12 angular locations measured in this paper (repeated across 3 rows) are shown in the forearm cross section of the right arm.

Force-displacement response from three trials of indentation at the 30 degree angular location on the first row.

Force-displacement response from three trials of indentation at the 30 degree angular location on the first row.

Force-displacement response at 6 angular locations on the first row of the forearm for a single human subject.

Force-displacement response at 6 angular locations on the first row of the forearm for a single human subject.

Force-displacement response with the forearm relaxed and flexed at two angular locations. Higher stiffness is observed at all angular locations during the flexed case when muscles are co-contracted.

Force-displacement response with the forearm relaxed and flexed at two angular locations. Higher stiffness is observed at all angular locations during the flexed case when muscles are co-contracted.

Viscoelastic relaxation response at two angles.

Viscoelastic relaxation response at two angles.

Indentation force in response to a sinusoidal input displacement at the 180◦ angular location.

Indentation force in response to a sinusoidal input displacement at the 180◦ angular location.

Human-centered approach for interface design in which interface padding properties are varied depending on stiffness measurements of the human limb.

Human-centered approach for interface design in which interface padding properties are varied depending on stiffness measurements of the human limb.

Controlled indentation displacement with force feedback is used in three types of applications on a human subject’s forearm. The soft tissue stiffness profile, viscoelastic relaxation behavior, and frequency domain response are measured. The ability to perform multiple characterizations with one indenter device broadens the scope of a human-centered approach to design, modeling, and perception as they relate to physical human-robot interfaces.

Contributions:

  • Engineered precision indentation system with stepper motor control (0.025mm resolution) and single-axis load cell (111mN resolution) for automated tissue characterization

  • Implemented 36-position angular positioning mechanism with 10-degree increments around human limbs using custom rotating ring structure and linear actuators

  • Developed multiple testing protocols in MATLAB including stiffness profiling, viscoelastic relaxation, and frequency response analysis for comprehensive tissue characterization

  • Validated measurement accuracy against ground-truth instrumentation, enabling repeatable characterization of human biomechanical properties across anatomical locations

Collaborators: Keya Ghonasgi, Paria Esmatloo, Ashish D. Deshpande

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