Comparative Design, Modeling, and Control Analysis of Robotic Transmissions
WOODS HOLE OCEANOGRAPHIC INSTITUTION MA
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Transmission dynamics are shown to dominate the stability and performance of impedance-and torque controlled rotary electro-mechanical systems where sensor and actuator are noncolocated. The experimental part of the analysis focuses on planetary, cycloidal, harmonic and cable reducers. Simple transmission models are proposed to model such effects as 1 transmission stiffness, 2 soft-zones and wind-up, 3 backlash and lost motion, and 4 stiction, friction and viscous losses. These models are experimentally verified using six different transmission types most commonly used in robot designs. Simple lumped-parameter linearnonlinear models are shown to predict stability margins and bandwidths fairly closely. Simple nonlinear lumped-and fixed- parameter models were unable to properly predict responses when the torque signals were of low-frequency and amplitude, underscoring the complexity in modeling the transmission-internal stick-slip phenomena. Transmission soft-zones are proven to reduce the stability margins of colocated impedance controlled and noncolocated torque-servoed electro-mechanical systems. None of the standard controller structures explored here could noticeably increase the system bandwidth of the closed loop system, without reducing the overall system performance. System damping, whether active or passive, as well as low pass filtering motor-controller signals, are shown to dramatically increase stability without having any effect on increasing system bandwidth.
- Physical and Dynamic Oceanography
- Electrical and Electronic Equipment
- Machinery and Tools