## 5 Discussion and Conclusions  
Using the suggested torque sensor, the measurement range is determined by the length of the moment arm in which the load cell is installed. Accordingly, the proposed torque sensor has the advantage of easy adjustment of the measurement range and sensitivity by changing the load cell position without further manufacturing or changing other components. However, what is clear is that, thanks to the structure of the adjustable moment arm, it can be modified immediately to have the required sensitivity or measurement range for users. For example, if the length of the moment arm is reduced from 1000 mm to 10 mm, the measurement range of this sensor decreases to 1/100, but the sensitivity increases by 100 times. Additionally, this is not the only advantage that the proposed torque sensor has due to its structural features. This sensor has the property of resisting other-axes torque/force structurally by applying the CRB. Additionally, the ball end bearings at both ends of the load cell transmit only pure axial force to the load cell, thereby fundamentally blocking the influence of other torque/force on the torque measurement. Resultantly, it is possible to accurately measure only the torque in the direction of interest. However, in return for gaining this huge advantage of adjustment, this sensor has distinct limitations. The most important specifications in the proposed torque sensor are directly affected by the arms length \(L\). By the relationship of \(F=\tau/L\), sensitivity of this sensor will be inversely proportional to \(L\). Consequently, in order to secure high sensitivity of the proposed sensor, a short \(L\) is required. The output resolution will decrease in inverse proportion to \(L\), like the sensitivity. Furthermore, the measurement range of this torque sensor is also directly affected by length \(L\). If the applied load cell is not changed, the measurement range increases in proportion to \(L\). Additionally, the long \(L\) lowers the physical natural frequency of the torque sensor with the weight of the load cell far from the center of rotation, which inevitably narrows its bandwidth. Excluding the motor part from the sensor prototype, the natural frequency of this sensor can be predicted by using the weight and stiffness of the load cell, lever arm and base arm. For example, it is calculated to have the natural frequencies of about 147 Hz and 116 Hz, respectively, when the load cell is integrated at a distance of 50 mm and 200 mm. Therefore, it will be reasonable to estimate the measurement bandwidth of this torque sensor prototype used in the experiment at the level of about 100 Hz. With a small-capacity load cell, it is possible to change a variety of measurement ranges, but it is difficult to simultaneously satisfy the specifications for high impact applications, such as high sensitivity, high bandwidth and wide measurement range. For the high impact applications, therefore, a huge-capacity load cell and a short moment arm with high bending stiffness will be essential. Figure 12: Measured torque according to the joint angle change for 5 times repetition between \(-50^{\circ}\) and \(30^{\circ}\). Consequently, in order to meet the required level of the sensor specifications, it is very important to properly select the arms length \(L\) together with the specifications of the utilized load cell itself. Despite the structural advantages of this torque sensor, the advantages were not conspicuously revealed in the previous experiments. In particular, it was difficult to confirm the change in sensitivity by changing the moment arm in the result of the second fundamental experiment. However, without a reference sensor, the new and simple method of evaluating the performance of the torque sensor using the weight rotation showed satisfactory results. It is also necessary to discuss the experimental method of measuring the performance of the torque sensor, which is not desirable but notable, used in this study.