Torque Ripple Analysis and Compensation of Servo Drives for Robot Application

Abstract: Permanent magnet synchronous motors or PMSMs are commonly used in multiple applications, both in industry and commercial use. These motors have many pros when compared to other electrical machines but do present the issue of torque ripple, especially cogging torque. One field that is particularly affected by this is industrial robotics applications as the control structures implemented and the physiological demands of the systems make the suppression of such ripple crucial. This paper attempts to documented and compensate the ripple of one such PMSM. This motor has presented an issue in its applications in robotics because of its ripple. By delving into machine design, motor drivers and control theory it is concluded that source of the ripple is not the commonly assumed cogging torque but rather magnetic saturation and core losses, expressing themselves through excitation of the sixth harmonic. The recommended solution to the issue is current injection which works by minimizing the effects of the harmonic. Some further work is also recommended, mainly to conclusively rule out possible fault source, such as the use of the same drive and more reliable mechanical construction.