The article introduces an integrated torque sensor within a harmonic drive reducer to accurately measure joint output torque， enhancing intelligent control and integration of collaborative robots. Using finite element analysis， the relationship between strain on the harmonic drive reducer's flexible wheel surface and torque is examined. A response surface model based on this analysis determines optimal grid structure parameters for the sensor， ensuring the best linear response. The sensor is designed using the Wheatstone bridge principle. Calibration and testing show a sensitivity of 0.249 mV/N·m， a linearity of 0.999 74， and a hysteresis error of 2.19%. With load torque changes from 0 to 70 N·m， the root mean square error is between 0.89 N·m and 0.98 N·m； for sinusoidal changes between ±70 N·m， it's 0.96 N·m to 1.05 N·m. This sensor accurately detects torque magnitude， aiding joint force control in collaborative robots and enhancing system integration.