Performance of Newly Developed Induction Motor with Built-in Torque Sensor (2nd Report)

A new type of induction motor with a built-in torque sensor has been developed for grinding torque monitoring. Sensitivity in the low torque range has been improved in order to detect small torque changes. The torque sensor utilizes a non-linear torsion spring to obtain both high-sensitivity and enough stiffness for grinding torque measurement. The main focus of the development is the possibility of using the torque sensor as a gap-eliminator. Experimental results obtained are as follows : (1) A narrow gap between a grinding wheel and workpiece in a static condition can be estimated from the grinding torque. However, the torque difference between a gap of 0μm and a gap of 40μm is only 0.08 N·m. This is only 0.3% of full scale of measuring range of the developed torque sensor. (2) The torque sensor has good linearity in torque measurement, and can be used for monitoring torque with proper consideration for drift and ripple. (3) The torque sensing motor performs as well as a conventional motor in grinding operations even though it has complicated rotor shaft system.