Neuromorphic Model of Reflex for Realtime Human-Like Compliant Control of Prosthetic Hand

Abstract

Current control of prosthetic hands is ineffective when grasping deformable, irregular, or heavy objects. In humans, grasping is achieved under spinal reflexive control of the musculotendon skeletal structure, which produces a hand stiffness commensurate with the task. We hypothesize that mimicking reflex on a prosthetic hand may improve grasping performance and safety when interacting with human. Here, we present a design of compliant controller for prosthetic hand with a neuromorphic model of human reflex. The model includes 6 motoneuron pools containing 768 spiking neurons, 1 muscle spindle with 128 spiking afferents, and 1 modified Hill-type muscle. Models are implemented using neuromorphic hardware with 1 kHz real-time computing. Experimental tests showed that the prosthetic hand could sustain a 40 N load compared to 95 N for an adult. Stiffness range was adjustable from 60 to 640 N/m, about 46.6% of that of human hand. The grasping velocity could be ramped up to 14.4 cm/s, or 24% of the human peak velocity. The complaint control could switch between free movement and contact force when pressing a deformable beam. The amputee can achieve a 47% information throughput of healthy humans. Overall, the reflex-enabled prosthetic hand demonstrated the attributes of human compliant grasping with the neuromorphic model of spinal neuromuscular reflex.

Evaluation of Model-Based Biomimetic Control of Prosthetic Finger Force for Grasp

“…Therefore, a reflex-model-based controller for hand prosthesis enables human-like capacity, which originally takes place in the spinal circuitry. Our pilot study has suggested the potential of mode-based controller for mimicking human hand control [1], which may lead to a unique approach for prosthetic control [23] among many other strategies [24]- [29].…”

“…Computational models of spinal reflex have been developed to prove the role of reflex in reaching [20] and holding [21]. On top of that, reflex-model-based prosthetic control has been attempted with success using neuromorphic hardware, a VLSI (very-large-scale-integrated-circuit) technology that leads to real-time computation of the reflex model [1]. On the neuromorphic hardware, it has been shown that proprio-motor signals can be engineered into biomimetic forms, i.e.…”

“…The precision and sensitivity of the force control were evaluated in a "press-without-break" task, which required the subject to press or grip a sensorized object with an expected range of force. Based on the same biomimetic controller [1], this paper refined the procedure of coupling between model and prosthetic hand in real-world. We hypothesized that the biomimetic controller may facilitate amputees for force control in the "press-withoutbreak" task with human operations.…”

Next-Generation Prosthetic Hand: from Biomimetic to Biorealistic

“…This technology has been applied to amputee control of prosthetic hand. Neuromorphic models of neuromuscular system: it is feasible to restore neuromuscular reflex process for cable-driven prosthetic hands with human-like traits, using neuromorphic hardware to perform fast computation of physiologically realistic models and to emulate human-like reflex in real time [ 6 ]. This technology is now in evaluation for human application.…”

“…Past research has accumulated a large body of knowledge on human sensorimotor system [ 9 , 23 – 26 ]. It is now technologically mature to translate this body of knowledge to design biorealistic prosthetic hands that restore neuromuscular mechanics [ 6 ], spinal reflexes [ 13 ], and tactile feedback [ 3 – 5 , 7 ]. This may result in not only superior performance but also a new generation of prosthetic hands.…”