Coordination of contact forces during multifinger static prehension.

Area of Science:

• Biomechanics
• Human motor control
• Robotics

Background:

• Understanding how humans control grip forces is crucial for designing advanced prosthetics and robotic grippers.
• Previous research has focused on individual force components, but a holistic view of force regulation is lacking.

Purpose of the Study:

• To investigate the effects of modifying normal or tangential finger forces on the entire set of contact forces during static object holding.
• To determine if internal force regulation in the human hand operates on a subset or the entirety of force components.

Main Methods:

• Subjects grasped a sensor-instrumented handle and performed three tasks: increasing grip force, spreading fingers, and squeezing fingers.
• Analysis focused on virtual finger (VF) forces, representing the combined force and moment of the four fingers.
• Statistical analysis was used to assess significant changes in normal and tangential VF forces.

Main Results:

• Statistically significant changes were observed in both normal and tangential virtual finger forces across all three tasks.
• The neutral point for tangential force during finger spreading/squeezing was located between the index and middle fingers.
• The effects of effort and torque on grip forces were additive, with no significant interaction, supporting the principle of superposition.

Conclusions:

• Internal forces in human prehension are regulated as a whole, involving coordinated adjustments in both normal and tangential components.
• This holistic regulation supports the principle of superposition, where the combined effect of different force components is the sum of their individual effects.
• Findings have implications for understanding human dexterity and informing the design of more sophisticated robotic manipulation systems.