Design and Simulation of a Passive Absorber to Reduce Measured Postural Tremor Signal.

Tremor is a semirhythmic oscillatory movement of a body part caused by alternating simultaneous contractions of an antagonistic muscle group. Medical and surgical treatments used to reduce the symptoms of involuntary tremor can cause negative side effects. This study examined the ability of passive vibration absorbers in reducing the amplitude of postural tremor (PT). Inertial measurement unit (IMU) was used to record PT signals at the forearm and hand of a patient. IMU signal was used to excite an upper limb modeled to represent the flexion-extension vibrational motion at the joints. Equations of motion were solved numerically to obtain a response that fits the measured tremor signal. Passive tuned mass damper (TMD) was modeled as a cantilever beam and a screw placed along its length, at a position reflecting its operational frequency. Natural frequency of the TMD was derived for different mass positions and validated numerically and experimentally. Modal damping ratio of the TMD, for each mass position, was also estimated. Mass position and damping coefficient of the TMD were optimized depending on the minimization in the power spectral density (PSD) of angular displacement amplitude at the wrist joint. Optimized three-TMD system of 28.64 g total effective mass with the estimated modal damping ratio reduced 83.1% of the PSD of the angular displacement amplitude. This study showed the performance ability of a lightweight passive absorber in controlling the involuntary tremor of a system excited by the measured tremor signal of a patient.

Tremor Reduction at the Palm of a Parkinson's Patient Using Dynamic Vibration Absorber.

Parkinson's patients suffer from severe tremor due to an abnormality in their central oscillator. Medications used to decrease involuntary antagonistic muscles contraction can threaten their life. However, mechanical vibration absorbers can be used as an alternative treatment. The objective of this study is to provide a dynamic modeling of the human hand that describes the biodynamic response of Parkinson's patients and to design an effective tuned vibration absorber able to suppress their pathological tremor. The hand is modeled as a three degrees-of-freedom (DOF) system describing the flexion motion at the proximal joints on the horizontal plane. Resting tremor is modeled as dual harmonic excitation due to shoulder and elbow muscle activation operating at resonance frequencies. The performance of the single dynamic vibration absorber (DVA) is studied when attached to the forearm and compared with the dual DVA tuned at both excitation frequencies. Equations of motion are derived and solved using the complex transfer function of the non-Lagrangian system. The absorber's systems are designed as a stainless steel alloy cantilevered beam with an attached copper mass. The dual DVA was the most efficient absorber which reduces 98.3%-99.5%, 97.0%-97.3% and 97.4%-97.5% of the Parkinson's tremor amplitude at the shoulder, elbow and wrist joint.