A Novel Virtual Torque Sensor for Rescue Robots with Harmonic Drives

Abstract

Abstract:In this paper, a method is developed for presenting a novel virtual torque sensor based on precise model and position measurements avoids the need of traditional strain gauges and amplifiers. More specifically, the harmonic drive compliance model and the Gaussian process regression (GPR) technique are used together to achieve virtual torque sensor measurement. While the harmonic drive compliance model provides the analytic part, the Gaussian process regression method is used to reconstruct the unmolded part based on motor-side and link-side joint angles as well as motor current. After an automatic offline calibration, the method allows for a lean online implementation. The virtual torque sensor measurement is compared with measurements of a commercial torque sensor, and the results have attested the effectiveness of the proposed method.

Simplified Sensorless Torque Estimation Method for Harmonic Drive Based Electro-Mechanical Actuator

“…The most recent torque estimation methods [2], [5] utilize ( 5)-( 8) for estimating the HDT torque T fs as follows:…”

“…This approach achieves good estimation results, but it requires an additional strain gauge sensor and signal conditioning hardware. The second approach is based on measuring flexspline torsion with two high-precision angular encoders at the input and output shafts of an HDT [2]- [5]. The encoder measurements are fed to a compliance model to estimate the applied torque.…”

“…This approach is a typical sensorless torque estimation concept because these encoders are already integrated into many robotic and motion control architectures. Recent studies for sensorless torque estimation include Vassileva et al [3], Zhang et al [2], and Xia et al [5].…”

“…Xia et al [5] reported significant torque errors for the torque estimation method previously developed by Zhang et al in [2]. Xia et al justified this deficiency because the compliance model in [2] cannot fully characterize the underlying torsion-torque dynamics.…”

“…In practical terms, the method reported by Xia et al [5] is complicated for many applications because it includes physical as well as data-based torque estimation methods. Many applications have limited computational resources that are mainly for primary motion control functions.…”