Simultaneous Control of Multiple Degrees of Freedom in Upper-Limb Prosthesis

Simultaneous Control of Multiple Degrees of Freedom in Upper-Limb Prosthesis

Presented by Michael Bornstein & Dr. Engeberg

Michael Bornstein

• Attending FAU
• Senior in Mechanical Engineering
• Participating in a REU hosted by I-SENSE

Current Prosthesis

• Expensive
• Not intuitive

Multitasking

Current prosthesis can only control a single degree of freedom at a time.

Electromyogram (EMG)

• Detects and quantifies muscle activation
• Most dual-site EMG use two preamplifier

Simultaneous Wrist Angle-Grasp Synergy (SWAGS) Controller

• Uses the sum and difference of the two electrodes
• Wider range of inputs
• Direct control- two analog inputs from 0 to +
• SWAGS- one analog input from - to + and one analog input from 0 to +

EMG Training

• New to EMG Poor performance
• Difficult to assess SWAGS if user has no prior EMG experience
• Short training set of eight, 66 second trials to familiarize users

Graph labeled Wrist Angle Tracking and Grasping Force

Error Metrics

How I define how well an individual performs

Left: Mean absolute error (smaller is better) with graph showing desired waveform and input difference

Right: % Power at desired frequency (larger at 0.2 Hz is better) with graph showing % power and frequency (Hz)

Frequency Spectrum Importance

Left: graph showing desired waveform, user input 1 and user input 2

Right: bar graph showing Mean absolute error for user input 1 and 2; total power at 0.2 Hz

The 2nd input has less mean absolute error than the 1st input, but is unusable as a control signal.

Training Results

• 8 IRB reviewed individuals
• Trials 1-3 only involve wrist tracking
• Trials 4-8 involve wrist tracking and grasping force

Left: Bar graph labeled Average Absolute Error; (smaller is better)

Right: Bar graph labeled % Total Power Found at 0.2 Hz; (larger is better)

Training Results

Bar chart labeled Force Threshold FAilures (total and mean)

Training greatly improves user's ability to hold an object without dropping it.

Post-Training Prosthetic Use

Image of prosthetic hand in lab setting

Conclusion

• SWAGS has the potential to be a computationally inexpensive EMG control scheme that allows simultaneous control of 2 degrees of freedom.
• Most people will not be able to use EMG effectively without any prior training.
• A short training regimen greatly improves user ability.

Future Work

• Completion of artificial neural network to determine direction of slip
• Completion of haptic feedback mechanism to alert user of slip

Questions?

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