Drag the sliders to move the dashed threshold lines. All scenarios below update instantly for both strategies.
Opening & closing strategies for a prosthetic hand
The prosthesis listens to two EMG channels. The red channel asks the hand to close, the green channel asks it to open. Each channel has a configurable activation threshold. When both channels are active at the same time, two different strategies can decide what the hand actually does. The charts below show five realistic signal pairs, side by side, for both strategies. The background colour of each chart marks the hand state at that instant; the timeline strip underneath repeats the same information with icons.
How the strategies work
Two EMG channels drive the prosthesis: the red signal commands Close, the green signal commands Open. Each channel has its own threshold (dashed line). The two strategies differ in how they pick a direction when both signals are active.
1 · Stronger signal
At every moment in time, look at both channels. If neither is above its threshold, the hand rests. If only one is above, that channel wins. If both are above, the channel with the larger amplitude wins. The direction can flip mid-burst as amplitudes change.
2 · First over
The first channel that crosses its threshold takes control of the hand. It keeps that control for as long as it stays above its threshold, regardless of what the other channel is doing. When it drops below, the hand goes idle until some channel crosses again.
Scenarios
Overlap — red dominates
Both channels activate around the same time and overlap; the red signal reaches a higher peak.
Observe: Stronger signal follows the amplitude (close wins). First over follows whichever channel crossed first.
Stronger signal
Direction follows whichever signal above its threshold has the larger value.
First over
Direction is locked to whichever signal crossed its threshold first, until it drops below.
Green crosses first, red peaks higher
Green crosses its threshold a moment before red, but red ends up with a larger amplitude.
Observe: Stronger signal switches to close mid-burst. First over keeps the hand opening until green falls below.
Stronger signal
Direction follows whichever signal above its threshold has the larger value.
First over
Direction is locked to whichever signal crossed its threshold first, until it drops below.
Clean sequence — green, then red
Green burst, return to rest, then a separate red burst.
Observe: Both strategies agree: open during the green burst, idle in between, close during the red burst.
Stronger signal
Direction follows whichever signal above its threshold has the larger value.
First over
Direction is locked to whichever signal crossed its threshold first, until it drops below.
Both hover near thresholds
Both signals oscillate close to their thresholds with similar amplitude.
Observe: Stronger signal flickers as the larger channel keeps swapping. First over locks onto whoever crossed first and stays calm.
Stronger signal
Direction follows whichever signal above its threshold has the larger value.
First over
Direction is locked to whichever signal crossed its threshold first, until it drops below.
Long green, brief red spike
A sustained green activation with a short red spike in the middle.
Observe: Stronger signal briefly switches to close during the spike. First over ignores the spike and keeps opening.
Stronger signal
Direction follows whichever signal above its threshold has the larger value.
First over
Direction is locked to whichever signal crossed its threshold first, until it drops below.