Method for Torsional Stiffness Coefficient Identification of a Manipulator Rotational Joint using an Inertial Measurement Unit

Knowledge of the manipulator’s joints and links stiffness parameters is often necessary for high-precision control in the presence of external loads. The article proposes a method for identifying torsion stiffness coefficient of a rotational joint of a 1-DOF manipulator using a microelectromechanical inertial measurement module (IMU) consisting of an accelerometer and an angular velocity sensor. The method is based on describing the dynamics of a joint with an unknown torsional stiffness coefficient using a transfer function (TF) with known input and output signals (the angle of rotation of the motor and the angle of rotation of the link, respectively). The input signal of the TF is read from the engine encoder, and the output signal is reconstructed from the data from the IMU. When harmonic signals with different frequencies are assigned to the drive, the amplitude change and phase shift of the signal passing through the system are measured. Based on the data obtained, the amplitude-phase frequency response of the system is constructed, from which the time constants of the TF describing this system are calculated. The time constants depend on the mechanical characteristics of the system, including the torsion stiffness coefficient of the virtual spring, which is calculated based on the identified time constants. The method, unlike the existing ones, does not require bulky equipment for applying external forces to the manipulator, nor expensive measuring systems for measuring displacements in space. The results of experimental validation on a 1-DOF manipulator confirm the workability of the proposed method.

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