The measurement of input and output torque of a precision reducer, the core component of an industrial robot, plays a vital role in evaluating the robot's performance. The TMSIS and TMSOS of a vertical cylindrical high-precision reducer detector were designed and investigated in this study to realize the accurate measurement of input and output torque of the reducer. Because a transmission chain connects the torque transducer and the reducer, the characteristics of the inevitable additional torque are analyzed in detail. A torque calibration device is developed to realize the calibration of the torque measurement system. The readings of the torque calibration device are compared with the data of the instrument’s torque measurement system to realize the instrument's torque calibration. The improved particle swarm optimization and Levenberg–Marquardt algorithm-based radial basis function neural network is used to compensate for the error of the torque measurement system. The parameters of the RBF neural network are settled according to the characteristics of the additional torque and the torque calibration results. The experimental results show that the torque measurement accuracy of the torque measurement system can reach 0.1% FS after torque calibration and error compensation.
The role of the functional diameter is very important to the thread fitting property; however, the main feature of the thread is the spiral surface in space, which has many parameters and is difficult to measure. To obtain a thread functional diameter more in line with the definition of the standard, an approach based on a compliant mechanism theory is presented for the design of a synthetic measurement probe, and a multi-degree of freedom (DOF) movement of the sensitive probing element is realized. High stiffness and high flexibility of the probe are achieved in the undesired direction and direction of freedom, respectively. A method in which the error source is analyzed is adopted to evaluate the measurement uncertainty. The expanded uncertainty of the thread functional diameter measurement is 0.008 mm (k = 2), which is due to the probe mechanism error motions.
To obtain a method for measuring thread functional diameter, a new probe based on the synthetic measurement principle is designed to quantify the practical effect of each parameter in all axial sections. The probing element is an axial slice of a standard thread with a certain thickness; hence, the slice has a determined lead angle and curvature radius. When threads with different diameters are measured by slices, the maximum error caused by the lead angle and curvature radius can approach 99 μm according to the simulation results. To solve this problem, a measurement error model is established by analyzing the relationship between the contact points of the measuring tip and thread. By simulations and experiments, our results show that most of the effect of lead angle and curvature radius can be compensated. Using six slices with different pitches, a precise detection of 192 kinds of threads is achieved after error compensation within the range of M65–M300.
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