Admittance-Based Voluntary-Driven Motion With Speed-Controlled Tremor Rejection

Abstract

In the elderly, there have been reports of above 10% of the population being diagnosed with pathological tremor. Some patients find the conventional medical solutions, which primarily include medications and surgery, insufficient to treat their conditions. Technologies to mechanically suppress tremor have been proposed as a potential alternative. Robotic solutions for suppressing human tremor typically revolve around identifying and isolating the tremor motion component. This work proposes instead to only estimate the intentional movement and reject any disturbance that interferes with such an intended movement. By designing the control feedback such that motions other than the voluntary are rejected, the tremor component is attenuated. The controller components include an outer loop admittance feedback loop and an internal velocity feedback loop. Additionally a state feedback is utilized to improve the velocity tracking. To test the proposed approach, a benchtop Tremor Simulation Device (TSD) was developed. The TSD consists of two motors, which respectively simulate the motion of a human joint and the suppressing action of a mechanical suppression system. A parametric stability analysis of the proposed tremor-suppression strategy is presented.A motion profile recorded from a person with tremor is used as human input in the TSD to experimentally validate the proposed tremor rejection strategy. Spectral analysis results show a 99.8% tremor reduction; the power reduction related to the voluntary movement is instead negligible (0.18%). Tracking of a velocity profile results in a small RMS error (0.58 rad/s). The manuscript concludes by comparing the proposed approach to others presented in the literature.

Need for mechanically and ergonomically enhanced tremor-suppression orthoses for the upper limb: a systematic review

“…Information not provided is marked with “?”#Orthosis name/GroupSupp. typeSuppression mechanismSuppression characteristicEfficacy [%] (method)Voluntary movement disturbanceEvaluation method(tremor disease or simulation)DOF coefficientTotal weight /one attenuator [kg]1Voluntary Driven OrthosisHernstadt [38–40]activeDirect drive motor [38–40]3 Nm [38–40]99.8 (PSD) [39, 40]0.15% (magnitude change) [39]test bench (1 ET/PD dataset) [38–40]1/1 (EFE) [38–40]0.875 / 0.334 [39]2EMG ExoskeletonFujie [41–44]activeDirect drive motor [41–44]??10.5% (not recognised movement) [42]?1/1 (EFE) [41–44]0.330 /? [42–44]3EMG Exoskeleton v2Fujie [45, 46]activeDirect drive motor [45, 46]1.3 Nm [45]50–80 (AA) [45, 46]no voluntary movement detection yet [45, 46]1 tremor subject (ET) [45, 46]1/4 (EFE) [45, 46]0.410 /?…”

“…Human muscle performance given as reference. Asterisk-tagged values are from external literature, since these data were not provided in the retrieved literatureRotary motor with transmission (#1, #4) [38–40, 47–56]Linear motor (#7) [59]Pneumatic piston-coil (#8) [60–64]Human muscle * [83, 84]Specific power [W/kg]117.5 (±3.7)387.3076.350Specific force/torque16.7 (±13.8) Nm/kg212.7 N/kg243.5 N/kg20 Nm/kgEnergy efficiency [%]55.8 (±4.2)85 * [85]20 * [86]35…”

Towards wearable tremor suppression using dielectric elastomer stack actuators

“…The drawbacks of medications and DBS motivate the development of alternative treatment options. One prospective alternative is wearable active mechanical tremor suppression, whereby actuators create exoskeleton-like systems that apply torques about joints to reduce tremor [9][10][11][12][13][14][15][16][17][18][19][20]. This approach has a major advantage over typical treatments: robust mechanical suppression of motion in the tremor range ensures effective treatment for any patient.…”

Voluntary-Driven Elbow Orthosis with Speed-Controlled Tremor Suppression

“…A state feedback was also incorporated to improve the speed controller tracking. The system being controlled as in Figure 3 can be shown to be stable (Herrnstadt and Menon, 2015 ). Several saturations were implemented with both the speed controller, limiting the acceleration/deceleration of the SM (± 23077 rpm/s), and with the force controller, limiting its output velocity into the speed controller (± 115 rpm).…”