A Torque-Sensor-Based Nonlinear Observer for Shockless Torque Control of Two-Inertia Systems with Backlash

Two-inertia resonant systems are used to represent several motion control systems with resonance modes such as drivetrains and robot joints, offering a more flexible approach for their control compared to single-inertia representations. Controlling the transmitted torsion torque (also known as joint torque) to the load allows to effectively control the driven load of the system regardless of the resonant mode, which can be done by employing torque sensors. However, many real systems contain some degree of joint backlash, which causes a large, impulse-like shock on torque reversals due to the mechanical play of the joint elements, which can lead to undesired behavior and even destruction of the mechanical elements of the system being controlled. While torque sensors are able to sense whether the drive and load-sides are in contact or not, they don't give information on the relative angle between both sides, which is necessary for achieving shockless torque control. This paper introduces a novel nonlinear observer structure based on torque sensing that is able to estimate all the load-side states even when backlash occurs. This new observer is then implemented in a torsion torque control scheme that employs model predictive control during backlash gap traversings to achieve shockless control. Simulation results confirm the effectiveness of this method.